Judy and Jill leave Jill's house at the same time. Judy drives north and Jill drives west. Judy's average speed is 6mph slower than Jill's.

Question

At the end of one hour, they are 85 miles apart. Find Jill's average speed.

Answer 1

85^2 = x^2 + (x-6)^2 = x^2 + x^2 -12x + 36 = 2x^2 -12x + 36

x^2 -6x + 18 = 85^2/2

(x-3)^2 = 85^2/2 -18 + 9 = 7225/2 - 9 = 3612.5 - 9 = 3603.5

x-3 = sqr3603.6

x = 3+ 60.02916 = 63.0 mph for Jill's speed, rounded off to nearest one-tenth

Judy is 6 mph slower = 57.0 mph

57^2 + 63^2 = 3249 + 3969 = 7218

sqr7218 = 85.0 rounded off to nearest one decimal