April 2016 (73E) Math

Can you explain the equation I need to write in order to solve problem #55? Thanks!

  1. Carrie and Manuel are side by side when they begin to run at the same time in the same direction around a track. Carrie runs at a constant rate of 30 seconds per lap, while Manuel runs at a constant rate of 50 seconds per lap. How many seconds after beginning to run will Carrie have run exactly 1 more lap than Manuel? A. 20 B. 40 C. 75 D. 80 E. 125

C.

Answer explanation:

Let the number of seconds after beginning to run be X;
let the number of laps run by Carrie be C;
let the number of laps run by Manuel be M.

Then, we have the following equations

(1) C = X / 30
(2) M = X / 50
(3) C = M + 1

Solving for the equations (1), (2) and (3), we have:

X / 30 = X / 50 + 1
X = 75


The complete answer explanations for the math section of Form 74E can be read here:
http://acthelper.com/act-form-73e-math-answer-explanations/

Can you send me the full test thanks!