Question

Phillip can do 15 math problems in 5 minutes. How long will it take him to do 21 math problems?

Answer 1

7 minutes

Explanation:

1. Set up a proportion:
   `(5)/(15) = (x)/(21)`
2. Cross multiply, then divide: 5 × 21 = 105, 105 ÷ 15 = 7
3. So, it takes Phillip 7 minutes to do 21 math problems

I hope this helps!

Answer 2

One math problem:5min divide 15＝0.3 min

21 math problem:21 x 0.3min＝6.3 min