Question

Lexie began making posters for the school awards banquet. She can make 6 posters per minute. Zach joined her 10 minutes after she started. He can make 7 posters per minute. Lexie continued to make 6 posters per minute. Together, they made 125 posters. How many posters did zach make?

Answer 1

10 * 6 = 60 by the time Zach joins so 125-60 = 65
Now 6 (lexie) +7 (zach)  = 13 (together) and 65/13 = 5. 
6*5 = 30 and 7*5 = 35. 35+30 = 65
Your answer is 5.