How to find A% of B = ___ using decimals (and mental math). Learnist Board: http://bit.ly/13AGhZq More information at http://bit.ly/ZXLw0I #P6

1. 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.

2. ‘of’ means multiplied by
70% of 800 = (.7)(800)
Change the percent to
the decimal form.
‘of’
becomes
‘times’

3. 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

4. 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

5. 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).

6. 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

7. 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.

8. Closing Notes
 Remember 