Percent of a Number with Decimals by Multiplying A% of B is __

To find A% of B:

You can multiply the numbers,

Then put the decimal point in the only logical place.

By Jim Olsen, W.I.U.#P6

‘of’ means multiplied by

70% of 800 = (.7)(800)

Change the percent tothe decimal form.

‘of’ becomes ‘times’

Example: Find 70% of 800.

• Ignore the zeros and decimal places.• Multiply 7 × 8 = 56• Put the decimal point in the only logical place.

– Here are the choices:

.56 5.6 56. 560. 5600.– The only one that is a reasonable answer is 560.,

because 70% needs to be between 50% and 100%. 50% of 800 would be 400. 560 is larger than 400.

70% of 800 = 560

Example: Find 70% of 8.

• Ignore the zeros and decimal places.• Multiply 7 × 8 = 56• Put the decimal point in the only logical place.

– Here are the choices:

.56 5.6 56. 560. 5600.– The only one that is a reasonable answer is 5.6,

because 70% needs to be between 50% and 100%. 50% of 8 would be 4; 5.60 is larger than 4.

70% of 8 = 5.6

Determine the decimal place by estimation and logic.

Some good benchmarks are:• 50% of the number (half of the number), • 10% of the number (1/10, move the decimal

place one place to the left), and • 1% of the number (1/100, move the decimal

place two places to the left).

This strategy/shortcut works great when one, or both, of the numbers have only

one non-zero digit.

More examples:

1. What is 6% of $30?

2. 35% of 200 is ___

Answers:

1. 6% of $30 = $1.80

2. 35% of 200 is 70

More examples:1. A bag of dog food

weighs 45 lbs. 2% of the dog food is sodium. How many pounds of sodium are there?

2. 40% of Steve’s investments are in stocks. He has $20,000 invested. How much is invested in stocks?

Answers:1. 2% of 45 = 0.9 lb.

2. 40% of 20,000 is $8,000.

Closing Notes

Remember

To find A% of B: You can multiply the numbers,

Then put the decimal point in the only logical place.

#P6