Hi Yuna.
First we should talk about a percent. It is the number asked for divided by the total.
So if they had asked for the percent of her throws that DID hit the dartboard, that would be
24. And since she had 30 throws, that is the total. So if we wanted the percent of her throws that DID hit the dartboard, it would be
24
--- = 0.8 To turn this into a percent, multiply by 100.
30
0.8 * 100 = 80%
NOW TO ANSWER YOUR QUESTION:
If she made 24 throws, how many did she miss? (30-24 = 6)
She MISSED 6 throws. So that percent would be
6
-- = 0.2 MULTIPLIED BY 100 = 20%
30
So the answer is 20%