Question

Maria walks at a rate of 3 meters per second on a moving walkway traveling at a speed of 1 meter per second in the opposite direction. Maria walks a distance d for t seconds until a security guard tells her she must move in the opposite direction. Which equation best represents this information?
A. d=2t
B. 4/t = d
C. d=4t
D. 2d=t

Answer 1

When you set up equations like this, look at the units for help. They cancel out during division and multiplication like numbers to give desired quantities. Rates can be reversed if need be (3 meters/sec or 1/3 sec/meter).

time × (distance / time) = distance
See.. time/time = 1;  leaving distance

Subtract the rate of the opposing walkway...
t × (3 m/s - 1 m/s) = d
2t = d

Answer is then A.