Machine X takes 7 minutes to cut 91 pieces of lumbers. Machine Y takes 10 minutes to cut 80 pieces of lumbers. Machine Z takes 15 minutes to cut 225 pieces of lumber. 

1. Which is the faster combination, X and Y or Y and Z? (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 X alone:
7 min → 91 pieces
1 min → 91 ÷ 7 = 13 pieces

Time taken by Machine Y alone:
10 min → 80 pieces
1 min → 80 ÷ 10 = 8 pieces

Time taken by Machine Z alone:
15 min → 80 pieces
1 min → 225 ÷ 15 = 15 pieces

Time taken by Machine X and Machine Y together:
1 min → 13 + 8 = 21 pieces

Time taken by Machine Y and Machine Z together:
1 min → 8 + 15 = 23 pieces

Machine Y and Z are the faster combination.

(b)
Number of more pieces of lumbers that can be cut by the faster combination (Machine Y and Z) in 1 minute
= 23 - 21
= 2 

Answer(s): (a) Y, Z or Z, Y; (b) 2