[問題]考古題 PS Form35 sec03-Q19

[achiachia]

A merchant paid $300 for a shipment of X identical calculators. The merchant used 2 of the calculators as demonstrators and sold each of the others for $5 more than the average cost of the X calculators. If the total revenue from the sale of the calculators was $120 more than the costs of the shipment, how many calculators were in the shipment?

A)24
B)25
C)26
D)28
E)30

the answer is E), 不好意思，請問怎麼算出來的？謝謝

[caspar]

A merchant paid $300 for a shipment of X identical calculators. The merchant used 2 of the calculators as demonstrators and sold each of the others for $5 more than the average cost of the X calculators. If the total revenue from the sale of the calculators was $120 more than the costs of the shipment, how many calculators were in the shipment?

A)24
B)25
C)26
D)28
E)30

the answer is E), 不好意思，請問怎麼算出來的？謝謝

2 of the calculators as demonstrators =>(X-2)
$5 more than the average cost of the X calculators=> $(300/X+5)
the total revenue =>420= 300 (shipping cost) + 120
Therefore,

(X-2)(300/X+5)=420
5X-130X-600=0
(5X-150)(X+4)=0
X=30 or -4

Ans: X=30

[achiachia]

謝謝您的解答！
不過，$5 more than the average cost of the X calculators=> $(300/X+5)........為什麼shipping cost 就是 cost of the X calculators呢？
calculators 本身不用成本？謝謝～～

[caspar]

謝謝您的解答！
不過，$5 more than the average cost of the X calculators=> $(300/X+5)........為什麼shipping cost 就是 cost of the X calculators呢？
calculators 本身不用成本？謝謝～～

Sorry!
It is my mistake.

$300 should be the total cost of the X calculators from a shipment of X identical calculators.

[achiachia]

看懂了～謝謝。