ISEE Middle Level Math : How to find the probability of an outcome

Study concepts, example questions & explanations for ISEE Middle Level Math

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Example Questions

Example Question #61 : Outcomes

Find the probability that we draw a 4 of Hearts from a deck of cards.

Possible Answers:

Correct answer:

Explanation:

To find the probability of an event, we will use the following formula:

 

So, given the event of drawing a 4 of Hearts, we can calculate the following:

Because there is only one 4 of Hearts in a deck of cards.

Now, we can calculate the following:

Because there are 52 cards we could potentially draw from a deck of cards.

 

Knowing this, we can substitute into the formula.  We get

 

Therefore, the probability of drawing a 4 of Hearts from a deck of cards is .

Example Question #61 : Probability

A bag contains the following:

  • 5 pens
  • 6 pencils
  • 7 markers

Find the probability of drawing a pencil from the bag.

Possible Answers:

Correct answer:

Explanation:

To find the probability of an event, we will use the following formula:

 

So, given the event of drawing a pencil from the bag, we can calculate the following:

Because there are 6 pencils in the bag.

Now, we can calculate the following:

Because there are 18 total items in the bag:

  • 5 pens
  • 6 pencils
  • 7 markers

 

Knowing this, we can substitute into the formula.  We get

 

Therefore, the probability of drawing a pencil from the bag is .

Example Question #61 : Probability

A bag contains the following:

  • 10 red pens
  • 15 black pens
  • 5 blue pens

Find the probability of drawing a black pen.

Possible Answers:

Correct answer:

Explanation:

To find the probability of an event, we will use the following formula:

 

So, given the event of drawing a black pen from the bag, we can calculate the following:

Because there are 15 black pens in the bag.

Now, we can calculate the following:

Because there are 30 total items in the bag to choose from:

  • 10 red pens
  • 15 black pens
  • 5 blue pens

 

Knowing this, we can substitute into the formula.  We get

Therefore, the probability of drawing a black pen from the bag is .

Example Question #64 : Outcomes

Find the probability of drawing a 3 from a deck of cards.

Possible Answers:

Correct answer:

Explanation:

To find the probability of an event, we will use the following formula:

 

So, given the event of drawing a 3 from a deck of cards, we can calculate the following:

Beause there are four 3s we could draw from a deck of cards

  •          3 of hearts
  •          3 of diamonds
  •          3 of clubs
  •          3 of spades

 

Now we can calculate the following:

Because there are 52 cards in the deck we could potentially draw.

 

Knowing this, we can substitute into the formula.  We get

Example Question #571 : Data Analysis And Probability

A bag contains the following:

 

  •          8 red crayons
  •          7 blue crayons
  •          4 green crayons
  •          5 yellow crayons

Find the probability you grab a green crayon from the bag.

Possible Answers:

Correct answer:

Explanation:

To find the probability of an event, we will use the following formula:

 

Now, given the event of grabbing  a green crayon from the bag, we can calculate the following:

Because there are 4 green crayons in the bag.

 

We can also calculate the following:

Because there are 24 total crayons we could potentially grab from the bag.

 

Knowing all of this, we can substitute into the formula.  We get

 

Therefore, the probability of grabbing a green crayon is .

Example Question #61 : Outcomes

A classroom contains the following:

  • 24 girls
  • 32 boys

Find the probability the teacher calls on a girl.

Possible Answers:

Correct answer:

Explanation:

To find the probability of an event, we will use the following formula:

 

Now, given the event of calling on a girl, we can determine:

because there are 24 girls in the class the teacher could call on.

 

We can determine:

because there are 56 total students in the class the teacher could potentially call on:

  • 24 girls
  • 32 boys

 

Now, we can substitute into the formula.  We get

 

Therefore, the probability the teacher calls on a girl is .

Example Question #61 : Outcomes

Find the probability of drawing a 7 from a deck of cards.

Possible Answers:

Correct answer:

Explanation:

To find the probability of an event, we will use the following formula:

 

So, given the event of drawing a 7 from a deck of cards we can calculate the following:

because there are four ways we can draw a 7 from the deck: 

  • 7 of clubs
  • 7 of spades
  • 7 of hearts
  • 7 of diamonds

Now, we can calculate the following:

because there are 52 cards we could potentially draw from a deck of cards.

 

Knowing this, we can substitute into the formula.  We get

 

Therefore, the probability of drawing a 7 from a deck of cards is .

Example Question #61 : Probability

Find the probability of drawing a heart from a deck of cards.

Possible Answers:

Correct answer:

Explanation:

To find the probability of an event, we will use the following formula:

 

So, given the event of drawing heart, we can calculate the following:

because there are 13 ways we can draw a heart:

  • Ace
  • Two
  • Three
  • Four
  • Five
  • Six
  • Seven
  • Eight
  • Nine
  • Ten
  • Jack
  • Queen
  • King

Now, we can calculate the following:

because there are 52 cards we could potentially draw from a deck of cards.

 

Knowing this, we can substitute into the formula.  We get

 

Therefore, the probability of drawing a heart from a deck of cards is .

Example Question #69 : Outcomes

A box contains the following:

  • 9 blue crayons
  • 3 green crayons
  • 4 red crayons
  • 1 yellow crayon

Find the probability of grabbing a red crayon from the box.

Possible Answers:

Correct answer:

Explanation:

To find the probability of an event, we will use the following formula:

 

Now, given the event of grabbing a red crayon from the box, we can calculate:

because there are 4 red crayons in the box we could grab.

 

We can also calculate:

because there are 17 total crayons we could potentially grab:

  • 9 blue crayons
  • 3 green crayons
  • 4 red crayons
  • 1 yellow crayon

 

So, we get

 

Therefore, the probability of grabbing a red crayon from the box is .

Example Question #61 : How To Find The Probability Of An Outcome

Find the probability that we draw a 5 from a deck of cards.

Possible Answers:

Correct answer:

Explanation:

To find the probability of an event, we will use the following formula:

 

So, given the event of drawing a 5, we can calculate the following:

because there are 4 ways we can draw a 5 from a deck:

  •          5 of clubs
  •          5 of spades
  •          5 of hearts
  •          5 of diamonds

Now, we can calculate the following:

because there are 52 cards we could potentially draw from a deck of cards.

 

Knowing this, we can substitute into the formula.  We get

 

Therefore, the probability of drawing a 5 from a deck of cards is .

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