Answer:
6 minutes
Step-by-step explanation:
Mr Crenshaw checks at a rate of 1/10 and Mr. Aguirre checks at a rate of 1/15.
If they work together, they will be checking at a combined rate of:
1/10 + 1/15 = [3(1) + 2(1)]/30
= 5/30 = 1/6
Their combined rate is 1/6 which means they check one set in 6 minutes