Machine D takes 9 minutes to cut 117 pieces of lumbers. Machine E takes 15 minutes to cut 150 pieces of lumbers. Machine F takes 8 minutes to cut 120 pieces of lumber. 

1. Which is the faster combination, D and E or E and F? (Eg A, B) 
2. In 1 minute, how many more pieces of lumbers can be cut by the faster combination compared to the other combination?

(a)
Time taken by Machine D alone:
9 min → 117 pieces
1 min → 117 ÷ 9 = 13 pieces

Time taken by Machine E alone:
15 min → 150 pieces
1 min → 150 ÷ 15 = 10 pieces

Time taken by Machine F alone:
8 min → 150 pieces
1 min → 120 ÷ 8 = 15 pieces

Time taken by Machine D and Machine E together:
1 min → 13 + 10 = 23 pieces

Time taken by Machine E and Machine F together:
1 min → 10 + 15 = 25 pieces

Machine E and F are the faster combination.

(b)
Number of more pieces of lumbers that can be cut by the faster combination (Machine E and F) in 1 minute
= 25 - 23
= 2 

Answer(s): (a) E, F or F, E; (b) 2