Question: a can do a work in 15 days and b in 20 days . if they work on it together for 4 days , then the fraction of the work that is left is :
A) 1 / 4
B) 1 / 10
C) 7 / 15
D) 8 / 15
E) 9 / 15
Correct answer: D
Grade: 7 | Topic: Ratios and proportions | Difficulty: Easy | Standard: 7.RP.A.3