PSAT Math : How to multiply decimals

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #492 : Arithmetic

45.728 x 3.2 = ?

Possible Answers:

1463.296

14632.96

146.3296

14.63296

146329.6

Correct answer:

146.3296

Explanation:

Multiply the numbers out in long format, then move the decimal point over the total number of decimal points in the two numbers (3 in the first, 1 in the second, so 4 total):

45.728 * 3.2 = 91456

91456 + 1371840 = 1,463,296 → 146.3296

Or just count the decimal points in the answer and make sure it's 4.

Example Question #1 : How To Multiply Decimals

At the farmer's market, oranges are $0.30 each, apples are $0.25 each, bananas are $0.40 each, and tomatoes are $0.60 each. If Scott buys 3 oranges, 7 apples, 4 bananas, and 8 tomatoes, how much does he spend?

Possible Answers:

$7.75

$11.40

$10.40

$9.05

$6.80

Correct answer:

$9.05

Explanation:

To find out how much Scott spends, we need to multiply the quantity of each fruit by its price and add them all up.

3 * $0.30 + 7 * $0.25 + 4 * $0.40 + 8 * $0.60 = $9.05

Example Question #421 : Arithmetic

\(\displaystyle y=\frac{49}{50}\times0.51\times52\)

If \(\displaystyle y\) is 25% of \(\displaystyle x\), what is the closest integer to the value of \(\displaystyle x\)?

Possible Answers:

\(\displaystyle {13}\)

\(\displaystyle 104\)

\(\displaystyle 208\)

\(\displaystyle 6.5\)

\(\displaystyle 26\)

Correct answer:

\(\displaystyle 104\)

Explanation:

We can approximate the value of y pretty quickly:

y ≈ 1(0.50)(52) = 26

Since y = 0.25x = (1/4)x we know that x  = 4y ≈ 4(26) = 104

Example Question #422 : Arithmetic

\(\displaystyle 0.5 \times 0.012 =\)

Possible Answers:

0.0006

0.006

6

0.6

0.06

Correct answer:

0.006

Explanation:

It's much easier to work with whole numbers, so we'll ignore the decimals for the first step: 5 x 12 = 60

Now look at the decimals. To add them back in, think of 60 as 60.0. Now move the decimal point four places to the left: 0.5 x 0.012 = .0060 = .006

 

Example Question #1 : How To Multiply Decimals

At the store, green fabric costs $4.53 a yard. How much does 3.8 yards of green fabric cost? (Round to two decimal places.)

Possible Answers:

$17.22

$17.21

$17.13

$17.12

$17.31

Correct answer:

$17.21

Explanation:

This is a simple multiplication problem involving decimals. Simply multiply 4.53 by 3.8:

\(\displaystyle \small 4.53*3.8 = 17.214\)

Now, round to the nearest two decimal places, giving an answer of 17.21.

Example Question #4 : How To Multiply Decimals

Find the product. Round to the nearest hundredths place.

\(\displaystyle 10.18 53\times 53.22\)

Possible Answers:

\(\displaystyle 541.8\)

\(\displaystyle 532.64\)

\(\displaystyle 541.78\)

\(\displaystyle 542\)

\(\displaystyle 500\)

Correct answer:

\(\displaystyle 541.78\)

Explanation:

The hundredths place is the position two places to the right of the decimal. Our product is \(\displaystyle 10.18 \times 53.22 = 541.7796\). Rounding to the hundredths place results in \(\displaystyle 541.78\).

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