ISEE Lower Level Math : Numbers and Operations

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

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Example Questions

Example Question #6 : How To Find A Ratio

A class of 40 students has 25 boys and 15 girls. Write the ratio of boys to girls in simplest form.

Possible Answers:

\(\displaystyle 8 \textrm{ to } 3\)

\(\displaystyle 5 \textrm{ to } 3\)

\(\displaystyle 8 \textrm{ to } 5\)

\(\displaystyle 25 \textrm{ to } 15\)

\(\displaystyle 5 \textrm{ to } 2\)

Correct answer:

\(\displaystyle 5 \textrm{ to } 3\)

Explanation:

The ratio of boys to girls is \(\displaystyle 25 \textrm{ to } 15\), but this is not in simplest form. Rewrite this as a fraction for simplicity, then divide both numbers by \(\displaystyle GCF (25,15) = 5\):

\(\displaystyle \frac{25}{15} = \frac{25\div 5}{15\div 5} = \frac{5}{3}\)

In simplest form, the ratio is \(\displaystyle 5 \textrm{ to }3\)

Example Question #7 : How To Find A Ratio

A total of 35 children took a poll about favorite breakfast foods, choosing between cereal, yogurt, and pancakes. If 14 preferred cereal and 7 preferred yogurt, how many preferred pancakes?

Possible Answers:

14

7

18

21

Correct answer:

14

Explanation:

To find the children who preferred pancakes, subtract all the other children (cereal + yogurt) from the total:

\(\displaystyle 14\: cereal+7\: yogurt=21\)

\(\displaystyle 35\: total-21\: children=14\: pancakes\)

Example Question #8 : How To Find A Ratio

Susan has a bag of 12 assorted candies that included 3 blue, 2 green, 4 red, and 3 yellow. If Susan picks one piece of candy without looking, which color has a 1 in 6 chance of being picked?

Possible Answers:

red

yellow and blue

green

yellow

blue

Correct answer:

green

Explanation:

There are 2 green candies in the assortment out of a total of 12 candies. The proportion of green candies to total candies is \(\displaystyle \frac{2}{12}\), which simplifies to \(\displaystyle \frac{1}{6}\). This fraction describes a 1 in 6 chance, which is what we are looking for. 

Example Question #1 : Ratio And Proportion

Determine the ratio of 86 to 129. 

Possible Answers:

\(\displaystyle 2:3\)

\(\displaystyle 2:43\)

\(\displaystyle 1:2\)

\(\displaystyle 3:43\)

Correct answer:

\(\displaystyle 2:3\)

Explanation:

Ratios represent how one number is related to another. These steps will help you determine the ratio of the numbers shown:

1) Divide both terms of the ratio by the GCF (greatest common factor). In this case, the GCF is 43 because 43 is the greatest number that goes into both numbers evenly. 

2) Show the ratio with a colon : and remember to keep the numbers in the same order!

Therefore, the ratio of 86 to 129 is \(\displaystyle 2:3\).

 

Example Question #9 : How To Find A Ratio

A truck with a tank that holds 24 gallons of gas gets 18 miles to the gallon. If the truck's gas gauge reads that the tank is one-half full, how many miles can it travel before it needs to be refueled?

Possible Answers:

\(\displaystyle 164 \textrm{ mi}\)

\(\displaystyle 216 \textrm{ mi}\)

\(\displaystyle 144 \textrm{ mi}\)

\(\displaystyle 432 \textrm{ mi}\)

\(\displaystyle 276 \textrm{ mi}\)

Correct answer:

\(\displaystyle 216 \textrm{ mi}\)

Explanation:

Multiply 18 miles per gallon by 24 gallons to get the distance the truck can travel on a full tank:

\(\displaystyle 18 \times 24 = 432\) miles

On one-half of a tank, this truck can travel 

\(\displaystyle 432 \times \frac{1}{2} = \frac{432}{2} = 216\ miles\)

Example Question #11 : How To Find A Ratio

A car with a tank that holds 15 gallons of gas gets 29 miles to the gallon. If the car's gas gauge reads that the tank is three-fourths full, how many miles can it travel before it needs to be refueled?

Possible Answers:

\(\displaystyle 44 \textrm{ mi}\)

\(\displaystyle 580 \textrm{ mi}\)

\(\displaystyle 326\frac{1 }{4} \textrm{ mi}\)

\(\displaystyle 435 \textrm{ mi}\)

\(\displaystyle 33 \textrm{ mi}\)

Correct answer:

\(\displaystyle 326\frac{1 }{4} \textrm{ mi}\)

Explanation:

Multiply 15 gallons by 29 miles per gallon to get the distance the car can travel on a full tank:

\(\displaystyle 15 \times 29 = 435\) miles.

Multiply this by three-fourths to get the distance it can travel on three-fourths of a tank.

\(\displaystyle 435 \times \frac{3}{4} = \frac{435 \times 3}{4}= \frac{1,305 }{4}\)

\(\displaystyle 1,305 \div 4 = 326 \textrm{ R }1\), so

\(\displaystyle \frac{1,305 }{4} = 326\frac{1 }{4}\) miles

Example Question #492 : Numbers And Operations

There are 24 pencils in a new box.  I have sharpened 18.  What is the ratio of unsharpened pencils to pencils in the new box?

Possible Answers:

\(\displaystyle 6\: to\: 24\)

\(\displaystyle 3\: to\: 4\)

\(\displaystyle 18\: to\: 24\)

\(\displaystyle 4\: to\: 3\)

\(\displaystyle 24\: to\: 18\)

Correct answer:

\(\displaystyle 6\: to\: 24\)

Explanation:

The ratio needed is unsharpened to new box and it says there are 24 pencils in a new box.  It does not say how many are unsharpened but it does give the amount that has been sharpened already.

To find the unsharpened amount subtract the number of pencils sharpened from the number of pencils in the new box.  Therefore, it would be \(\displaystyle 24\, -\, 18= 6\) unsharpened pencils.

 The ratio of unsharpened to new box would be \(\displaystyle 6\: to\: 24\).

Example Question #493 : Numbers And Operations

There are 32 computers in the lab and 30 students from the science class might be using them for a project today.  When it is lab time, 15 students are NOT ready to go. 

What is the ratio of students that are NOT ready for lab to students in the science class?

Possible Answers:

\(\displaystyle 15\: to \: 32\)

\(\displaystyle 1\: to \: 2\)

\(\displaystyle 2\: to \: 1\)

\(\displaystyle 30\: to \: 32\)

None of the other answers.

Correct answer:

\(\displaystyle 1\: to \: 2\)

Explanation:

The question asked for the ratio of the students NOT ready for lab to the students in the science class.

There are 15 students that are not ready for the computer lab.

There are 30 students in the science class.

Therefore, the ratio is \(\displaystyle 15 \: to\: 30\).

Since 15 and 30 can be reduced by their greatest common factor of 15 the ratio is simplified to \(\displaystyle 1\: to \: 2\).   

 

\(\displaystyle [\frac{15}{15} = 1\)  \(\displaystyle and \: \: \frac{30}{15} = 2]\)

Example Question #494 : Numbers And Operations

A cake recipe asks for 4 cups of flour and 1 cup of sugar. If Sarah only has 2 cups of flour, how much sugar should she use?

Possible Answers:

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

\(\displaystyle 2\textup{ cups}\)

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

\(\displaystyle \frac{1}{8}\textup{ cup}\)

\(\displaystyle 1\textup{ cup}\)

Correct answer:

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

Explanation:

In order to solve this problem, we should set up a ratio.

The ratio of flour to sugar in the recipe is \(\displaystyle 4:1\)

If Sarah only has 2 cups of flour, the ratio would be \(\displaystyle 2:x\) where \(\displaystyle x\) is the sugar.

Looking at the first ratio, 2 cups is half of 4, so the sugar would also be half. So the answer is \(\displaystyle \frac{1}{2}\) cup of sugar.

 

Example Question #491 : Numbers And Operations

Mrs. Steven's class has a female-to-male student ratio of 3:2. If the class has 18 female students, how many male students are there?

Possible Answers:

\(\displaystyle 8\ students\)

\(\displaystyle 12\ students\)

\(\displaystyle 14\ students\)

\(\displaystyle 15\ students\)

\(\displaystyle 22\ students\)

Correct answer:

\(\displaystyle 12\ students\)

Explanation:

The ratio of female-to-male students is 3:2 or:

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

Since we have 18 female students, we can set it up like this:

\(\displaystyle \frac{3}{2}=\frac{18}{x}\)

where \(\displaystyle x\) is the unknown number of male students.

Now multiply the fraction by whatever number so that the numerator (the female students) equals 18.

\(\displaystyle \frac{3\times 6}{2\times 6}=\frac{18}{12}\)

So the amount of male students is 12.

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