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Ratios & Percentages

Ratios & Percentages

At a Glance - Estimating Percentages

Most of the time in life, you will estimate percents. You probably won’t bust out a pen and paper every time you need to pay a tip or figure out the discount on a shirt. If you get good at estimating percents, you’ll get close enough.

The first thing to do is round the amount to a nice easy number to work with.

Shortcuts for Estimating Percentages

%Trick Round Amount Estimate
10% Move the decimal one place to the left $72.38 -> $70.00
$58.20 -> $60.00
$26.00 -> $25.00
10% of $70.00 is $7.00
10% of $60.00 is $6.00
10% of $25.00 is $2.50
20% Double 10% $72.38 -> $70.00
$58.20 -> $60.00
$26.00 -> $25.00
20% of $75.00 is $15.00
20% of $60.00 is $12.00
20% of $25.00 is $5.00
25%Round amount to a number divisible by 4, then divide the amount in fourths$72.38 -> $72.00
$58.20 -> $60.00
$26.00 -> $28.00
25% of $72.00 is $18.00
25% of $60.00 is $15.00
25% of $28.00 is $7.00
50% Cut the amount in half $72.38 -> $72.00
$58.20 -> $60.00
$28.00 -> $28.00
50% of $72.00 is $36.00
50% of $60.00 is $30.00
50% of $28.00 is $14.00

Do the following problems in your head. Feel free to round the numbers.

Estimating Percentages Exercise 1

10% of $92.86


Estimating Percentages Exercise 2

50% of $131.90


Estimating Percentages Exercise 3

25% of $76.75


Estimating Percentages Exercise 4

20% of $14.09


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