Dina leaves her house driving east at 35 miles per hour. Thirty minute later, her husband John notices she forgot her cell phone and sets off after her. How fast must John travel in order to catch up with Dina 2 hours after he leaves?

Answer: John must travel at 43.75 mph

Step-by-step explanation:

Let x represent how fast John should travel in order to catch up with Dina 2 hours after he leaves.

By the time they meet, they would have covered the same distance.

Distance = speed * time

Dina leaves her house driving east at 35 miles per hour. Distance covered by Dina in 2 hrs 30 minutes is

35 * 2.5 = 87.5 miles

Thirty minute later, her husband John notices she forgot her cell phone and sets off after her.

Distance travelled by John in 2 hours is x * 2 = 2x

Since they covered the same distance, then

2x = 87.5

x = 87.5/2 = 43.75