What have you done?
I've been at them now for over an hour, googled it, asked tutors, short of asking my professor I can't figure it out. Here they are:
Joelle is determined to get some exercise and walks to the store at a brisk rate of 4.5 mph. She meets her friend at the store, and together they walk back at a slower rate of 3mph. Joelles total walking time is 1 hr.
a. How long did it take her to walk to the store?
b. What is the distance to the store?
the book has the answer as 0.04 hr (24 minutes) for a. and 1.8 mi for b. No matter how I set it up I cannot come up with 0.04
the second one:
An elevator can accomodate a maximum weight of 2000lb. If four passengers on the elevator have an average weight of 180 lb each, how many additional passengers of the same weight can the elevator carry before the maximum weight capacity is reached?
The answer is 7, but how do I set it up to get the correct answer?
Since both speeds are known, there are two choices to choose the unknown: either time or distance. In the first case, there are two unknown times: to the store and back. Let us denote them by x and y. Then the distance to the store is both 4.5x and 3y. In addition, x + y = 1, which gives you two equations with two variables.
Alternatively, let x be the distance to the store. Then x / 4.5 is the time spent walking to the store and x / 3 is the time spent walking back, so x / 4.5 + x / 3 = 1.
After finding either of the two times or the distance and knowing both speeds, it is easy to compute the distance or, correspondingly, the times.