Malia runs 5 miles in 1 hour. how many miles does she run in half an hour? in 2 1/2 hours?

OK so you take the 5 miles in one hour and divide that by 2 to find the half hour
x=5/2   x= 2.5 miles 

To find the 2 1/2 hours you take the hour distance (5) double it and add the half hour distance
x=(5 x 2) + 2.5   x= 10 + 2.5    x=12.5 miles