Davie and Horatio are riding their motorbikes on a scenic tour that is 80 miles long. Davie rides at 20 miles per hour and leaves 90 minutes before Horatio. How fast must Horatio ride to finish at the same time as Davie?

Davie takes 80 ÷ 20 = 4 hours to complete the tour. Horatio starts 90 minutes, or 1.5 hours, later, so he has 4 − 1.5 = 2.5 hours to cover the same 80 miles. His speed must be 80 ÷ 2.5 = 32 mph, so the correct choice is 32 mph.

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