Let last week's production = N.
Pay rule:
If N ≤ 36
Pay = NX
If N > 36
Pay = 36X + (3/2)X(N − 36)
Need N.
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(1)
Total pay last week = 480
NX = 480 if N ≤ 36
or
36X + (3/2)X(N − 36) = 480 if N > 36
Many (N, X) pairs work.
Example:
N = 30, X = 16
N = 40, X = 10
Not sufficient.
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(2)
This week:
Production = N + 2
Pay = 510
Again many possibilities.
Example:
If N = 28, then this week production = 30
30X = 510
X = 17
Works.
If N = 38, then this week production = 40
36X + 4(3/2)X = 42X = 510
X = 85/7
Works.
Different N values.
Not sufficient.
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(1) + (2)
Pay increased from 480 to 510.
Increase = 30.
Since production increased by 2 items, check where the two weeks lie relative to 36.
Case 1: Both weeks ≤ 36
Increase = 2X
2X = 30
X = 15
Then
NX = 480
N = 32
Works.
Case 2: Last week = 36, this week = 38
Increase = 2 × (3/2)X = 3X
3X = 30
X = 10
Last week's pay = 36X = 360, not 480.
Impossible.
Case 3: Both weeks > 36
Increase = 2 × (3/2)X = 3X
3X = 30
X = 10
Last week's pay = 480
36(10) + (3/2)(10)(N − 36) = 480
360 + 15(N − 36) = 480
N − 36 = 8
N = 44
Works.
We get N = 32 or N = 44.
Both satisfy both statements.
Not sufficient.
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Answer: E
GMAT shortcut:
From (1)+(2), pay rose by $30 when production rose by 2 items.
If both weeks are at or below 36 items:
2X = 30 ⇒ X = 15 ⇒ N = 480/15 = 32.
If both weeks are above 36 items:
3X = 30 ⇒ X = 10 ⇒ N = 44.
Two different values of N are possible.
Answer = E.