ISEE Lower Level Quantitative : How to find a ratio

Study concepts, example questions & explanations for ISEE Lower Level Quantitative

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Example Questions

Example Question #1 : How To Find A Ratio

Stacy has started collecting coins.  She has twice as many wheat pennies as she does 1946 dimes, and three times as many 1983 quarters as she does 1946 dimes.  If Stacy has \(\displaystyle \small 4\) 1946 dimes, what is the ratio of wheat pennies to 1983 quarters?

Possible Answers:

\(\displaystyle \small 2:3\)

\(\displaystyle \small 12:4\)

\(\displaystyle \small 4:3\)

\(\displaystyle \small 12:8\)

\(\displaystyle \small 8:12\)

Correct answer:

\(\displaystyle \small 2:3\)

Explanation:

We know that Stacy has \(\displaystyle \small 4\) 1946 dimes.

We also know that she has twice as many wheat pennies, so we must multiply \(\displaystyle \small 4\) by \(\displaystyle \small 2\) to find the total number of wheat pennies.

\(\displaystyle \small 4\cdot 2=8\)

We also know that Stacy has three times as many 1986 quarters, so we multiply \(\displaystyle \small 4\) by \(\displaystyle \small 3\) to find the total number of 1986 quarters.

\(\displaystyle \small 4\cdot 3=12\)

Now our ratio of wheat pennies to 1986 quarters is \(\displaystyle \small 8:12\), but this can be simplified because both numbers are divisible by \(\displaystyle \small 4\).

\(\displaystyle \small (8/4)=2\)

\(\displaystyle \small (12/4)=3\)

So our ratio becomes \(\displaystyle \small 2:3\)

Example Question #2 : How To Find A Ratio

Cassie works a four hour shift at the coffee shop.  During her shift, \(\displaystyle \small 37\) customers order coffee, \(\displaystyle \small 27\) order orange juice, and \(\displaystyle \small 15\) order hot choclate.  What is the ratio of customers who order orange juice to those who order coffee?

Possible Answers:

\(\displaystyle \small 27:37\)

\(\displaystyle \small 15:37\)

\(\displaystyle \small 27:15\)

\(\displaystyle \small 37:15\)

\(\displaystyle \small 2:3\)

Correct answer:

\(\displaystyle \small 27:37\)

Explanation:

Since there are \(\displaystyle \small 27\) customers who order orange juice, \(\displaystyle \small 27\) is the first number of our ratio. 

The second number of our ratio is \(\displaystyle \small 37\), because \(\displaystyle \small 37\) people order coffee. 

Therefore, our ratio is :

\(\displaystyle \small 27:37\)

Example Question #1 : How To Find A Ratio

Steve is having a birthday party. So far, he has invited thirty-nine of his friends from school, fifteen of whom are girls. He wants to make the ratio of girls to boys at the party two to one. How many more girls does he need to invite, assuming no more boys are invited? 

Possible Answers:

\(\displaystyle 35\)

\(\displaystyle 33\)

\(\displaystyle 65\)

\(\displaystyle 0\)

\(\displaystyle 63\)

Correct answer:

\(\displaystyle 35\)

Explanation:

Counting Steve, there are forty attendees so far, fifteen of whom are girls and twenty-five of whom (including Steve) are boys. To obtain a two-to-one girl to boy ratio, he needs to invite a total of fifty girls, so he needs to invite thirty-five more.

Example Question #4 : How To Find A Ratio

Scott's mother bakes 12 cookies and he eats half of them. Scott's mom then puts red frosting on 4 cookies and blue frosting on the rest of the cookies. What is the ratio of cookies with red frosting to cookies with blue frosting?

Possible Answers:

\(\displaystyle 1:4\)

\(\displaystyle 2:1\)

\(\displaystyle 1:2\)

\(\displaystyle 4:1\)

Correct answer:

\(\displaystyle 2:1\)

Explanation:

If Scott's mother bakes 12 cookies and he eats half of them, that means he will eat 6 cookies, leaving 6 uneaten cookies.

If Scott's mom then puts red frosting on 4 cookies and blue frosting on the rest of the cookies, 2 cookies will get blue frosting. (\(\displaystyle 4+2=6\)). 

Therefore, the ratio of cookies with red frosting to cookies with blue frosting is \(\displaystyle 4:2\), which is equal to \(\displaystyle 2:1\).

Example Question #2 : How To Find A Ratio

For every 3 peanuts in a bag of trail mix, there are 1 chocolate chip and 2 raisins. What is the proportion of raisins in the mix?

Possible Answers:

\(\displaystyle \frac{1}{3}\)

\(\displaystyle \frac{2}{5}\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle \frac{1}{4}\)

Correct answer:

\(\displaystyle \frac{1}{3}\)

Explanation:

Given that there are 3 peanuts for every 1 chocolate chip and 2 raisins, the proportion of raisins can be found by dividing the number of raisins by the sum of all the items in the mix. This results in:

\(\displaystyle \frac{2}{3+1+2}=\frac{2}{6}=\frac{1}{3}\)

Therefore, \(\displaystyle \frac{1}{3}\) is the correct answer. 

Example Question #1 : Ratio And Proportion

Jose is \(\displaystyle 3\) times taller than his baby brother Michael. If Jose is \(\displaystyle 48\) inches tall, how tall is Michael? 

Possible Answers:

\(\displaystyle 8\) inches

\(\displaystyle 24\) inches

\(\displaystyle 16\) inches 

\(\displaystyle 14\) inches

Correct answer:

\(\displaystyle 16\) inches 

Explanation:

The ratio of Jose to Michael's height is \(\displaystyle 3:1\).

Thus, if Jose is \(\displaystyle 48\) inches taller than Michael must be \(\displaystyle 3\) times shorter.

We can write this as the expression, \(\displaystyle \frac{48}{3}=16\).

Also, an equivalent ratio for \(\displaystyle 3:1\) = \(\displaystyle 48:16\).

Example Question #1 : How To Find A Ratio

Find an equivalent ratio. 

\(\displaystyle 15:3\)

Possible Answers:

\(\displaystyle 1:5\)

\(\displaystyle 1:3\)

\(\displaystyle 3:1\)

\(\displaystyle 5:1\)

Correct answer:

\(\displaystyle 5:1\)

Explanation:

An equivalent ratio of \(\displaystyle 15:3\) is \(\displaystyle 5:1\).

This is the furthest simplification of the ratio. 
The greatest common divisor is needed to simplify the expression.

Both \(\displaystyle 15\) and \(\displaystyle 3\) are divisible by \(\displaystyle 3\), \(\displaystyle \frac{15}{3}=5\)  and  \(\displaystyle \frac{3}{3}=1\).

Thus, the correct answer is \(\displaystyle 5:1\)

Example Question #3 : Ratio And Proportion

Solve for \(\displaystyle x\)

\(\displaystyle 9:27=19:x\)

Possible Answers:

\(\displaystyle x= 57\)

\(\displaystyle x=3\)

\(\displaystyle x=\frac{19}{3}\)

\(\displaystyle x=41\)

Correct answer:

\(\displaystyle x= 57\)

Explanation:

To solve this problem the relationship between the two numbers in the first ratio needs to be established.

Since, \(\displaystyle 27\) is \(\displaystyle 3\) times larger than \(\displaystyle 9\), an equivalent ratio must have the same relationship.

Thus, \(\displaystyle x\) must be \(\displaystyle 3\) times larger than \(\displaystyle 19\), and \(\displaystyle 19\cdot 3=57\) 

Thus, \(\displaystyle 9:27=19:57\)

Example Question #5 : Ratio And Proportion

There are \(\displaystyle 36\) students in a fifth grade class. If there are \(\displaystyle 12\) girls in the class, what is the ratio of the number of boys in the class to the total number of students in the class?

Possible Answers:

\(\displaystyle \frac{7}{8}\)

\(\displaystyle \frac{3}{4}\)

\(\displaystyle \frac{3}{2}\)

\(\displaystyle \frac{2}{3}\)

Correct answer:

\(\displaystyle \frac{2}{3}\)

Explanation:

First, find the number of boys in the class by subtracting the number of girls in the class from the total number of students.

\(\displaystyle \text{Number of boys}=36-12=24\)

Now, we know that the ratio of the number of boys in the class to the total number of students in the class is \(\displaystyle 24\text{ to }36\).

We can express that ratio as the following fraction:

\(\displaystyle \frac{24}{36}=\frac{2}{3}\)

Example Question #3 : Ratio And Proportion

There are \(\displaystyle 40\) students in a computer science class. If there are \(\displaystyle 15\) boys in the class, what is the ratio of the number of girls in the class to the total number of students in the class?

Possible Answers:

\(\displaystyle \frac{5}{8}\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle \frac{3}{4}\)

\(\displaystyle \frac{7}{10}\)

Correct answer:

\(\displaystyle \frac{5}{8}\)

Explanation:

First, find the number of girls in the class by subtracting the number of boys in the class from the total number of students.

\(\displaystyle \text{Number of girls}=40-15=25\)

Now, we know that the ratio of the number of boys in the class to the total number of students in the class is \(\displaystyle 25\text{ to }40\).

We can express that ratio as the following fraction:

\(\displaystyle \frac{25}{40}=\frac{5}{8}\)

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