Michael and his sister Jane left their house at the same time going in the opposite direction. Michael drove at an average speed of

Question

40 mph, while Jane drove at an average speed of 35 mph. After how many hours were they 400 miles apart?

Answer 1

Michael's distance --- x
Jan'e distance ---- 400-x

x/40 = (400-x)/35

35x = 16000 - 40x

solve for x, the distance that Michael went

divide x by 40 to get the time,
(check by dividing 400-x by 35, you must get the same answer)

Answer 2

d1 + d2 = 400.
40*T + 35*T = 400,
T = 5 1/3 Hours.