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

x^2 + (x+6)^2 = 85^2 = 7225

x^2 + x^2 + 12x + 36 = 7225

2x^2 +12x = 7189

x^2 + 6x = 7189/2

x^2 +6x + 9 = 7189/2 +9

(x+3)^2 = 7207/2

x+3 = sqr(7207/2)

x = sqr(7207/2) - 3 = about 57 mph for slower Judy

Jill = x+6 = about 63 mph

57^2 +63^2 = 7218 = about 85^2 = 7225