Physics
posted by Sean .
A golfer rides in a golf cart at an average speed of 3.10 m/s for 23.0 s. She then gets out of the cart and starts walking at an average speed of 1.30 m/s. For how long (in seconds) must she walk if her average speed for the entire trip, riding and walking, is 2.00 m/s?

d1 = 3.1 m/s * 23 s = 71.3 m.
V(ave) = (d1 + d2) / (t1 + t2),
2 = (71.3 + 1.3 * t2) / (23 + t2),
Cross multiply:
46 + 2t2 = 71,3 + 1,3t2,
Solve for t2:
2t2  1,3t2 = 71.3  46,
0.7t2 = 25.3,
t2 = 36.1 s. = Seconds walked.