How to multiply decimals

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PSAT Math › How to multiply decimals

Questions 1 - 6
1

If is 25% of , what is the closest integer to the value of ___?

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

2

6

0.6

0.06

0.006

0.0006

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

3

45.728 x 3.2 = ?

146.3296

1463.296

14632.96

146329.6

14.63296

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.

4

Find the product. Round to the nearest hundredths place.

Explanation

The hundredths place is the position two places to the right of the decimal. Our product is . Rounding to the hundredths place results in .

5

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.)

$17.21

$17.22

$17.12

$17.31

$17.13

Explanation

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

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

6

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?

$9.05

$10.40

$6.80

$7.75

$11.40

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

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