How do you do estimate by using percents?

Answer 1

Say you've just eaten a decent meal with some good service at a decent restaurant and you want to tip your waitress 18%, but the bill comes to $37.62.

In order to estimate what 18% is of that bill, first calculate what 10% of it is, which can be easily done by moving the decimal place over to the left by one. 10% of $37.62 is $3.76. Next, find out what 20% of the bill is by doubling this last number. 20% of $37.62 = 2 X 10% of $37.62 = 2 X $3.76 = $7.52. Now, you know that 18% must fall somewhere between $3.76 and $7.52, and in fact, you know that it will fall closer to the larger value than the smaller. Therefore, a tip of $6.50 seems like a pretty good estimate of what you were trying to do.

Let's double check.

$6.50/$37.62 = 17.3%. So, we weren't exact, but we were close, and all we did was estimate using percentages, and trust me, the waitress will be happy with that tip!