Step by step
The question
Question: A town has 8,000 people.
The number drops 10%, then drops 10% again.
How many people live there now?
1 Down 10% of 8,000
Percent means out of 100.
So 10% is 10 out of 100.
That is the same as 1 out of 10: one tenth.
To find 10%, we divide by 10.
8,000 divided by 10 is 800.
Down 10% means we take away 800.
8,000 minus 800 is 7,200.
2 Down 10% of 7,200
Now the number is 7,200.
The second 10% is not of the old number.
It is 10% of the new number, 7,200.
To find 10%, we divide by 10.
7,200 divided by 10 is 720.
Down 10% means we take away 720.
7,200 minus 720 is 6,480.
Careful!
We can't just add the percents.
The second percent is of a new number.
So the new number is 6,480.
3 Check
Let's check another way: down 10% leaves 100% minus 10%.
That is 90% of the number.
90% is 90 out of 100: 0.9.
8,000 times 0.9 is 7,200.
Then: down 10% leaves 100% minus 10%.
That is 90% of the number.
90% is 90 out of 100: 0.9.
7,200 times 0.9 is 6,480.
The same.
So the answer is right!
Let's look back.
First: down 10% of 8,000.
Then: down 10% of 7,200.
Last: check.