Step by step
The question
Question: A farm has 600 sheep.
The number grows 20%, then drops 25%.
How many sheep are there now?
1 Up 20% of 600
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.
600 divided by 10 is 60.
20% is 2 times 10%.
2 times 60 is 120.
Up 20% means we add 120.
600 plus 120 is 720.
2 Down 25% of 720
Now the number is 720.
The second 25% is not of the old number.
It is 25% of the new number, 720.
To find 10%, we divide by 10.
720 divided by 10 is 72.
20% is 2 times 10%.
2 times 72 is 144.
5% is half of 10%.
Half of 72 is 36.
25% is 20% plus 5%.
144 plus 36 is 180.
Down 25% means we take away 180.
720 minus 180 is 540.
Careful!
We can't just add the percents.
The second percent is of a new number.
So the new number is 540.
3 Check
Let's check another way: up 20% makes it 100% plus 20%.
That is 120% of the number.
120% is 120 out of 100: 1.2.
600 times 1.2 is 720.
Then: down 25% leaves 100% minus 25%.
That is 75% of the number.
75% is 75 out of 100: 0.75.
720 times 0.75 is 540.
The same.
So the answer is right!
Let's look back.
First: up 20% of 600.
Then: down 25% of 720.
Last: check.