d=distance; r=rate; and t=time. The applicable formula is d=rt. In this problem we know d and t and need only solve d=rt for r, the rate (speed):
d/t = r
2 3/4 becomes 11/4; 1 hr and 15 min becomes 1.25 hours. The speed is thus r
(11 mile)/4
r = ---------------------- = (11/4)(5/4) mph = (55/16) mph
1.25 hour
If you wished, you could re-write this as 4 7/16 mph.
