Understand Additive Inverses

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7th Grade Math › Understand Additive Inverses

Questions 1 - 10
1

What is the additive inverse (opposite) of $-12$?

$0$

$\frac{1}{12}$

$-12$

$12$

Explanation

This question tests understanding of additive inverses: opposite quantities (a and -a) that combine to zero (a+(-a)=0), occurring when opposite transactions, changes, or directions cancel. The additive inverse of a is -a: a number with the opposite sign that sums to zero (7 and -7: 7+(-7)=0, mutually inverse); in contexts like depositing $50 and withdrawing $50 summing to $0 net change (opposite transactions cancel), temperature rising 8° and falling 8° giving 0° net change (opposite changes cancel), or gaining 15 yards and losing 15 yards resulting in 0 net yards (opposite directions cancel); every number has an additive inverse: 5→-5, -3→3 (flip sign), 2.5→-2.5, even 0→0 (zero is its own inverse). For example, the number -12 has an inverse of 12 since -12 + 12 = 0. The correct inverse here is 12, as it flips the sign of -12 to make the sum zero. A common error is claiming the inverse of -12 is still -12 (not flipping the sign), or confusing it with the reciprocal 1/12, which is the multiplicative inverse where -12 × (1/-12) = 1, not additive. Finding the additive inverse involves flipping the sign (-12→12), and verifying means checking if they sum to zero (-12 + 12 = 0, yes). Properties include the inverse being unique (only 12 adds with -12 to give 0), and avoiding mistakes like claiming the sum is not zero.

2

A thermometer shows a temperature increase of $8^\circ$C in the morning and a decrease of $8^\circ$C in the afternoon. What is the total change in temperature for the day?

$16^\circ$C

$8^\circ$C

$0^\circ$C

$-16^\circ$C

Explanation

This question tests understanding of additive inverses: opposite quantities (a and -a) that combine to zero (a+(-a)=0), occurring when opposite transactions, changes, or directions cancel. The additive inverse of a is -a: a number with the opposite sign that sums to zero (7 and -7: 7+(-7)=0, mutually inverse); in contexts like depositing $50 and withdrawing $50 summing to $0 net change (opposite transactions cancel), temperature rising 8° and falling 8° giving 0° net change (opposite changes cancel), or gaining 15 yards and losing 15 yards resulting in 0 net yards (opposite directions cancel); every number has an additive inverse: 5→-5, -3→3 (flip sign), 2.5→-2.5, even 0→0 (zero is its own inverse). For example, a temperature rise of 8°C is +8, a fall of 8°C is -8, and combined: 8 + (-8) = 0 net change (back to starting temperature). The total change is 0°C because the increase and decrease are additive inverses that cancel. A common error might be adding absolute values to get 16°C or halving to 8°C, or wrongly claiming -16°C by doubling the negative, but opposites sum to zero. Finding the additive inverse involves flipping the sign (+8→-8), and verifying means checking if they sum to zero (8 + (-8) = 0, yes). In contexts like weather, opposite changes neutralize, and the property is commutative: +8 + (-8) = (-8) + 8 = 0.

3

A student deposits $35 into a school store account and later withdraws $35. What is the net change in the account balance?

$-35

$0

$35

$70

Explanation

This question tests understanding of additive inverses: opposite quantities (a and -a) that combine to zero (a+(-a)=0), occurring when opposite transactions, changes, or directions cancel. The additive inverse of a is -a: a number with the opposite sign that sums to zero (7 and -7: 7+(-7)=0, mutually inverse); in contexts like a deposit of $50 and withdrawal of $50 summing to $0 net change (opposite transactions cancel), temperature rising 8° and falling 8° giving 0° net change (opposite changes cancel), or gaining 15 yards and losing 15 yards resulting in 0 net yards (opposite directions cancel); every number has an additive inverse: 5→-5, -3→3 (flip the sign), 2.5→-2.5, even 0→0 (zero is its own inverse). For example, a deposit of $35 is modeled as +35, and a withdrawal of $35 as -35, combined: 35 + (-35) = 0 net (back to starting balance). In this case, the net change in the account balance is $0, as the deposit and withdrawal are additive inverses that cancel each other out. A common error might be thinking the net is $70 by adding the absolute values or claiming -35, confusing the withdrawal as the final balance. To find the additive inverse, simply flip the sign (5→-5, -3→3, 0→0), and verify by checking if a + b = 0 (if 7 + (-7) = 0, yes inverses; if 7 + 5 = 12 ≠ 0, not inverses). In real-world contexts like bank accounts, a deposit of $100 and withdrawal of $100 leave the balance unchanged (opposites neutralize), and remember the property that the inverse is unique (only one number adds with 35 to give 0: must be -35).

4

A student deposits $\$25$ into a school store account and later withdraws $$25$. What is the net change in the account balance? (Think of withdrawal as a negative change.)

$25$

$-25$

$0$

$50$

Explanation

This question tests understanding of additive inverses: opposite quantities (a and -a) that combine to zero (a+(-a)=0), occurring when opposite transactions, changes, or directions cancel. The additive inverse of a is -a: a number with the opposite sign that sums to zero (7 and -7: 7+(-7)=0, mutually inverse); in contexts like a deposit of $50 and withdrawal of $50 summing to $0 net change (opposite transactions cancel), temperature rising 8° and falling 8° giving 0° net change (opposite changes cancel), or gaining 15 yards and losing 15 yards resulting in 0 net yards (opposite directions cancel); every number has an additive inverse: 5→-5, -3→3 (flip sign), 2.5→-2.5, even 0→0 (zero is its own inverse). For example, a deposit of $25 is modeled as +25, and a withdrawal of $25 as -25, combined: 25 + (-25) = 0 net (back to starting balance). In this case, the net change is $0, as the deposit and withdrawal are additive inverses that cancel each other out. A common error is thinking the net is $50 by adding magnitudes without signs (25 + 25 = 50) or confusing with multiplication, but actually, opposites sum to zero. To find an additive inverse, flip the sign (like 25 → -25). You can verify by checking if they sum to zero: 25 + (-25) = 0, confirming they are inverses; in real-world contexts like bank accounts, a deposit and equal withdrawal leave the balance unchanged.

5

A hiker climbs $200$ meters up a trail and then goes $200$ meters back down to the starting elevation. Which expression shows the net change in elevation?

$-200 + (-200) = -400$

$200 \times(-200) = -40{,}000$

$200 + 200 = 400$

$200 + (-200) = 0$

Explanation

This question tests understanding of additive inverses: opposite quantities (a and -a) that combine to zero (a+(-a)=0), occurring when opposite transactions, changes, or directions cancel. The additive inverse of a is -a: a number with the opposite sign that sums to zero (7 and -7: 7+(-7)=0, mutually inverse); in contexts like depositing $50 and withdrawing $50 summing to $0 net change (opposite transactions cancel), temperature rising 8° and falling 8° giving 0° net change (opposite changes cancel), or gaining 15 yards and losing 15 yards resulting in 0 net yards (opposite directions cancel); every number has an additive inverse: 5→-5, -3→3 (flip sign), 2.5→-2.5, even 0→0 (zero is its own inverse). For example, climbing +200 m and descending -200 m: 200 + (-200) = 0 net change (back to start). The correct expression is 200 + (-200) = 0, showing the net elevation change as zero due to additive inverses. A common error is using multiplication like 200 × (-200) = -40,000 (confusing operations) or adding positives to 400 (ignoring signs), but additive inverses involve addition to zero. Finding the additive inverse involves flipping the sign (200→-200), and verifying means checking if they sum to zero (200 + (-200) = 0, yes). In hiking contexts, up and down are opposites that cancel when equal.

6

A student deposits $30 into a school store account and later withdraws $30. What is the net change in the account balance?

$-60

$0

$30

$60

Explanation

This question tests understanding of additive inverses: opposite quantities (a and -a) that combine to zero (a+(-a)=0), occurring when opposite transactions, changes, or directions cancel. The additive inverse of a is -a: a number with the opposite sign that sums to zero (7 and -7: 7+(-7)=0, mutually inverse); in contexts like depositing $50 and withdrawing $50 summing to $0 net change (opposite transactions cancel), temperature rising 8° and falling 8° giving 0° net change (opposite changes cancel), or gaining 15 yards and losing 15 yards resulting in 0 net yards (opposite directions cancel); every number has an additive inverse: 5→-5, -3→3 (flip sign), 2.5→-2.5, even 0→0 (zero is its own inverse). For example, a deposit of $30 is modeled as +30, a withdrawal of $30 as -30, and combined: 30+(-30)=0 net (back to starting balance). In this case, the net change is $0 because the deposit and withdrawal are additive inverses that cancel each other out. A common error might be thinking the net is $60 by adding the absolute values without considering signs, or confusing it with $30 by halving, but actually, opposites cancel to zero. Finding the additive inverse involves flipping the sign (like +30→-30), and verifying means checking if they sum to zero (30 + (-30) = 0, yes). In real-world contexts, such as bank accounts, a deposit and equal withdrawal leave the balance unchanged, demonstrating how opposites neutralize each other.

7

What is the value of $-(-9)$?

$0$

$-9$

$-18$

$9$

Explanation

This question tests understanding of additive inverses: opposite quantities (a and -a) that combine to zero (a+(-a)=0), occurring when opposite transactions, changes, or directions cancel. The additive inverse of a is -a: a number with the opposite sign that sums to zero (7 and -7: 7+(-7)=0, mutually inverse); in contexts like depositing $50 and withdrawing $50 summing to $0 net change (opposite transactions cancel), temperature rising 8° and falling 8° giving 0° net change (opposite changes cancel), or gaining 15 yards and losing 15 yards resulting in 0 net yards (opposite directions cancel); every number has an additive inverse: 5→-5, -3→3 (flip sign), 2.5→-2.5, even 0→0 (zero is its own inverse). For example, the additive inverse of 9 is -9, so -(-9) applies the negative sign to -9, flipping it back to 9, since -(-9) = 9. The value is 9, as taking the negative of a negative number gives the positive (the additive inverse of -9 is 9). A common error is keeping it negative like -9 (not flipping) or doubling to -18 (confusing with multiplication), or claiming 0 (misunderstanding), but -(-a) = a. Finding the additive inverse involves flipping the sign (-9→9), and verifying means checking if -9 + 9 = 0, yes. Properties include the inverse being unique, and this shows double negation returns the original.

8

Are $-9$ and $9$ additive inverses? (In other words, do they add to $0$?)

No, because $-9 \times 9 = -1$.

No, because $-9 + 9 = 18$.

Yes, because $-9 + 9 = 0$.

Yes, because $-9$ is the reciprocal of $9$.

Explanation

This question tests understanding of additive inverses: opposite quantities (a and -a) that combine to zero (a+(-a)=0), occurring when opposite transactions, changes, or directions cancel. The additive inverse of a is -a: a number with the opposite sign that sums to zero (7 and -7: 7+(-7)=0, mutually inverse); in contexts like a deposit of $50 and withdrawal of $50 summing to $0 net change (opposite transactions cancel), temperature rising 8° and falling 8° giving 0° net change (opposite changes cancel), or gaining 15 yards and losing 15 yards resulting in 0 net yards (opposite directions cancel); every number has an additive inverse: 5→-5, -3→3 (flip the sign), 2.5→-2.5, even 0→0 (zero is its own inverse). For example, -9 and 9 sum to -9 + 9 = 0, so they are additive inverses. Yes, -9 and 9 are additive inverses because -9 + 9 = 0. A common error is confusing with multiplication like -9 × 9 = -81 or claiming the sum is 18 by adding absolutes, or mixing with reciprocal where 1/9 × 9 = 1. To find the additive inverse, simply flip the sign (5→-5, -3→3, 0→0), and verify by checking if a + b = 0 (if -9 + 9 = 0, yes inverses; if -9 + (-9) = -18 ≠ 0, not). Avoid mistakes like confusing additive and multiplicative inverses (a + (-a) = 0 vs. a × (1/a) = 1 are different), or claiming the sum is non-zero.

9

Which number must be added to $\dfrac{3}{4}$ to make $0$?

$-\dfrac{4}{3}$

$\dfrac{4}{3}$

$-\dfrac{3}{4}$

$\dfrac{3}{4}$

Explanation

This question tests understanding of additive inverses: opposite quantities (a and -a) that combine to zero (a+(-a)=0), occurring when opposite transactions, changes, or directions cancel. The additive inverse of a is -a: a number with the opposite sign that sums to zero (7 and -7: 7+(-7)=0, mutually inverse); in contexts like a deposit of $50 and withdrawal of $50 summing to $0 net change (opposite transactions cancel), temperature rising 8° and falling 8° giving 0° net change (opposite changes cancel), or gaining 15 yards and losing 15 yards resulting in 0 net yards (opposite directions cancel); every number has an additive inverse: 5→-5, -3→3 (flip the sign), 2.5→-2.5, even 0→0 (zero is its own inverse). For example, the number 3/4 has an inverse of -3/4 since 3/4 + (-3/4) = 0. The number that must be added to 3/4 to make 0 is -3/4, as it is the additive inverse. A common error is confusing with the reciprocal 4/3, which is the multiplicative inverse (3/4 × 4/3 = 1), not additive, or claiming 3/4 itself where the sum is not zero. To find the additive inverse, simply flip the sign (5→-5, -3→3, 0→0), and verify by checking if a + b = 0 (if 3/4 + (-3/4) = 0, yes; if 3/4 + 4/3 ≠ 0, not). Properties include commutativity (3/4 + (-3/4) = (-3/4) + 3/4 = 0), and avoid claiming the sum is non-zero or using the wrong sign.

10

Which statement about additive inverses is true?

Additive inverses multiply to $0$.

Every number has an additive inverse, and $a + (-a) = 0$.

Only positive numbers have additive inverses.

The additive inverse of $-3$ is $-3$.

Explanation

This question tests understanding of additive inverses: opposite quantities (a and -a) that combine to zero (a+(-a)=0), occurring when opposite transactions, changes, or directions cancel. The additive inverse of a is -a: a number with the opposite sign that sums to zero (7 and -7: 7+(-7)=0, mutually inverse); in contexts like a deposit of $50 and withdrawal of $50 summing to $0 net change (opposite transactions cancel), temperature rising 8° and falling 8° giving 0° net change (opposite changes cancel), or gaining 15 yards and losing 15 yards resulting in 0 net yards (opposite directions cancel); every number has an additive inverse: 5→-5, -3→3 (flip sign), 2.5→-2.5, even 0→0 (zero is its own inverse). For example, every number like -3 has an inverse of 3, since -3 + 3 = 0. The true statement is that every number has an additive inverse, and a + (-a) = 0. A common error is thinking inverses multiply to 0 or that only positives have them, but they add to 0 and all numbers do. To find an additive inverse, flip the sign. Verifying: check sum to zero; mistakes confuse with multiplicative inverses.

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