How to multiply negative numbers

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ACT Math › How to multiply negative numbers

Questions 1 - 7
1

Evaluate 3x3 + x2 if x = _–_2

14

_–_22

_–_20

28

Explanation

When multiplying a negative number an odd number of times, the answer is negative. When multiplying a negative number an even number of times, the answer is positive. Order of operations also applies: Parentheses, Exponents, Multiplication and Division, Addition and Subtraction, from left to right. A mnemonic to remember the order of operations is “Please excuse my dear Aunt Sally.”

3(_–2)3 + (–_2)2

= 3(_–_8) + (4)

= _–_24 + 4

= _–_20

2

Evaluate the following:

Explanation

Two odd numbers multiplied always result in an even number. Simply multiple the two as though they were even. Thus

3

If a = –2 and b = –3, then evaluate a3 + b2

1

8

9

17

5

Explanation

When multiplying negative numbers, we get a negative answer if there are an odd number of negative numbers being multiplied. We get a positive answer if there are an even number of negative numbers being multiplied.

a3 + b2 becomes (–2)3 + (–3)2 which equals –8 + 9 = 1

4

Evaluate:

–3 * –7

–21

10

–10

21

4

Explanation

Multiplying a negative number and another negative number makes the product positive.

5

Simplify the following expression: (–4)(2)(–1)(–3)

12

–16

–24

24

Explanation

First, we multiply –4 and 2. A negative and a positive number multiplied together give us a negative number, so (–4)(2) = –8. A negative times a negative is a positive so (–8)(–1) = 8. (8)(–3) = –24.

6

Evaluate.

\dpi{100} \small (-8\times 6) - (5\times -3)

\dpi{100} \small -33

\dpi{100} \small -63

\dpi{100} \small 62

\dpi{100} \small 33

\dpi{100} \small 32

Explanation

\dpi{100} \small (-8\times 6) - (5\times -3)

Multiplying a negative and a positive number creates a negative product:

\dpi{100} \small (-48)-(-15)

\dpi{100} \small -48+15

\dpi{100} \small -33

7

Solve.

(6-8)\times 11=

-22

22

13

-13

5

Explanation

(6-8)=-2

-2\times 11=-22

A negative number multiplied by a positive number will always be negative.

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