Machine Q takes 10 minutes to cut 100 pieces of lumbers. Machine R takes 20 minutes to cut 160 pieces of lumbers. Machine S takes 12 minutes to cut 168 pieces of lumber. 

1. Which is the faster combination, Q and R or R and S? (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 Q alone:
10 min → 100 pieces
1 min → 100 ÷ 10 = 10 pieces

Time taken by Machine R alone:
20 min → 160 pieces
1 min → 160 ÷ 20 = 8 pieces

Time taken by Machine S alone:
12 min → 160 pieces
1 min → 168 ÷ 12 = 14 pieces

Time taken by Machine Q and Machine R together:
1 min → 10 + 8 = 18 pieces

Time taken by Machine R and Machine S together:
1 min → 8 + 14 = 22 pieces

Machine R and S are the faster combination.

(b)
Number of more pieces of lumbers that can be cut by the faster combination (Machine R and S) in 1 minute
= 22 - 18
= 4 

Answer(s): (a) R, S or S, R; (b) 4