10. The price of a product is $a. Bill bought s products and then sold 80 percents of them $b. which of the following represents the whole deal if Billâ€™s profit was three times the cost?
(a) 0.8sb = 4sa.
(b) (1-0.8)s â€“ab = 3s.
(c) 3(0.8a â€“ sb) = sa.
(d) (s-0.8s)(b-a) = 3.
(e) (s0.8s) / (b-a) = 3.
I have a bit hard time to get the question right. There are 2 blindpoints that are confusing me:
1. Bill bought s products and then sold 80 percents of "s products" $b. Does this mean each unit is sold for $b or total amount of the selling of this 80% s products $b?
2. "...if Bill's profit is three times the cost", does this mean three times the cost of all s units of this product or three times the cost of 80% of this product?
Let's say each unit is sold for $b, and it is three times the cost of that 80% units
Initially Bill bought s units of this particular item for $a each, so total cost of all units is "a*s". Bill sold 80% of these units, and the cost for these 80% units is "0.8*a*s".
He sold each unit for $b per pcs, and he sold 80% of them; so the total selling price for this 80% is "0.8*s*b".
Total profit is revenue - cost = 0.8sb-0.8as. This profit is three times the cost of all s units.
So 0.8sb-0.8as=3*0.8as, 0.8sb-0.8as=2.4as, 0.8sb=2.4as
and there is no matching answer.