GRE Math : How to multiply decimals

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #11 : Decimals

find 0.72

Possible Answers:

0.049

49

4.9

0.49

0.0049

Correct answer:

0.49

Explanation:

0.7 * 0.7 = 0.49

Trick: do the numbers without the decimals (7*7)

49; move the decimal of the answer the total number of spaces per each number (one for each 0.7)

0.49

Example Question #1 : How To Multiply Decimals

There are 3,500 people in group A and 5,000 people in group B:

Car Type

% in Group A Who Own

% in Group B Who Own

Motorbike

 4

 9

Sedan

 35

 25

Minivan

 22

 15

Van

 9

 12

Coupe

 3

 6

The number of people in group B who own a minivan is how much greater or less than the number of people in group A who own a minivan?

Possible Answers:

50 fewer

30 fewer

15 more

30 more

20 fewer

Correct answer:

20 fewer

Explanation:

In this question, simply take the percentage of each group that owns a minivan and compare the values. For minivans we look at the middle row which we recognize as a percent that must be converted to a decimal. Acknowledge that there's a different number of people between the groups A and B:

Group B: 0.15(5000) = 750

Group A: 0.22(3500) = 770

750 – 770 = –20; thus, group B has 20 fewer people who own minivans than group A.

Example Question #2 : How To Multiply Decimals

Given that , which best describes the relationship between , and ?

Possible Answers:

Correct answer:

Explanation:

We must recognize that if x and y are both between 0 and 1, then they must be fractions (decimals). To determine their relationships, we can substitute values for x and y. Let's have and (because y must be greater than x).

If x and y are both between 0 and 1, then xy is also between 0 and 1 (though smaller than either x or y individually).

The value of (xy)2 will be less than (xy), since squaring any number between 0 and 1 gives a smaller result.

Finally,  is largest, since dividing a larger number by a smaller one gives a result greater than 1.

Note that the substituted values for x and y were purely hypothetical; any values that satisfy the given inequality could be used.

Example Question #3 : How To Multiply Decimals

You bought a dozen eggs marked at  and received  change from . What is the percent of sales tax?  

Possible Answers:

Correct answer:

Explanation:

Set the equation up as 

 

Solve for , which equals  

or

Therefore the percent sales tax is: 

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