One way to do this problem is to construct a formula. Randi’s pay is equal to $2,000 plus commission:
P = 2000 +...

The question only asks about Randi’s pay in months in which she sells more than 10 forklifts, so she will definitely be receiving 5% commission on 10 forklifts that each cost s. Since the revenue from the forklifts would then be 10s, Randi’s commission would be 0.05(10s), or 0.5s:
P = 2,000 + 0.5s +...

Now, add the commission for the forklifts she sells above the first 10. Since these first 10 forklifts are already accounted for, denote the forklifts at this commission level by writing f – 10. Since each
forklift still costs s, the revenue from these forklifts would be s(f – 10). Since Randi receives 10% of this as commission, the amount she receives would be 0.10s(f – 10):
P = 2,000 + 0.5s + 0.10s(f – 10)

It is possible to simplify further by distributing 0.10s(f – 10), but before doing more work, check the answers—answer choice (E) is already an exact match.


Alternatively, plug in numbers. Say forklifts cost $100 (so, s = 100). Randi makes $5 each for the first 10 she sells, so $50 total. Then she makes $10 each for any additional forklifts. Pick a value for f
(make sure the value is more than 10, since the question asks for a formula for months in which Randi sells more than 10 forklifts). So, in a month in which she sells, for example, 13 forklifts (so, f = 13), she would make $2,000 + $50 + 3($10) = $2,080.

In this example:
s = 100
f = 13

Plugin these values for s and f to see which choice yields $2,080.

Only choice (E) works:
P = 2,000 + 0.5(100) + 0.10(100)(13 – 10)
P = 2,000 + 50 + 10(3)
P = 2,080