Step by step
The question
Question: A $300 phone goes down 20%, then down 10%.
What is the new price?
1 Down 20% of $300
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.
$300 divided by 10 is $30.
20% is 2 times 10%.
2 times $30 is $60.
Down 20% means we take away $60.
$300 minus $60 is $240.
2 Down 10% of $240
Now the price is $240.
The second 10% is not of the old number.
It is 10% of the new number, $240.
To find 10%, we divide by 10.
$240 divided by 10 is $24.
Down 10% means we take away $24.
$240 minus $24 is $216.
Careful!
We can't just add the percents.
The second percent is of a new number.
So the new price is $216.
3 Check
Let's check another way: down 20% leaves 100% minus 20%.
That is 80% of the price.
80% is 80 out of 100: 0.8.
$300 times 0.8 is $240.
Then: down 10% leaves 100% minus 10%.
That is 90% of the price.
90% is 90 out of 100: 0.9.
$240 times 0.9 is $216.
The same.
So the answer is right!
Let's look back.
First: down 20% of $300.
Then: down 10% of $240.
Last: check.