SOLUTION: A man bought a used computer for $80, repaired it, and sold it for $143, thus making a profit of 30%. How much did he spend on repairs?

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Question 1118808: A man bought a used computer for $80, repaired it, and sold it for $143, thus making a profit of 30%. How much did he spend on repairs?
Found 2 solutions by Theo, ikleyn:
Answer by Theo(13342) (Show Source):
You can put this solution on YOUR website!

profit = revenue minus cost.

profit ratio = (revenue minus cost) / cost.

percent profit = profit ratio * 100.

profit ratio = percent profit / 100.

the revenue is equal to 143.

the cost is equal to 80 plus the cost of repairing the computer.

the percent profit is 30%.

the profit ratio is equal to 30% / 100 = .3.

let x equal the cost of repairing the computer.

the total cost is therefore 80 + x.

revenue= 143.
cost = 80 + x

profit = revenue minus cost = 143 - (80 + x) = 143 - 80 - x = 63 - x.

profit ratio = (revenue - cost) / cost.

since profit ratio = .3 and revenue - cost = 63 - x and cost = 80 + x, profit ratio equation becomes:

.3 = (63 - x) / (80 + x).

multiply both sides of this equation by (80 + x) to get:

.3 * (80 + x) = 63 - x.

simplify to get:

24 + .3 * x = 63 - x

add x to both sides of this equation and subtract 24 from both sides of this equation to get:

x + .3 * x = 63 - 24.

combine like terms to get:

1.3 * x = 39

divide both sides of this equation by 1.3 to get:

x = 39 / 1.3 = 30.

this means the cost of repairing the computer is 30.

you have:

cost of the computer is 80.
cost of repairing the computer is 30.
total cost is 80 + 30 = 110.

revenue is 143.

profit is (revenue minus cost) = 143 - 110 = 33.

profit ratio is equal to profit / cost = 33 / 110 = .3

percent profit = profit ratio * 100 = 30%.

solution looks good.

solution is that he spent 30 dollars on repairing the computer.

Answer by ikleyn(52816) (Show Source):
You can put this solution on YOUR website!
.

Let x be the amount he spent on repair. Then you have this equation = 0.3 Simplify and solve for x 143 - (80+x) = 0.3*(80+x) 143 - 80 - x = 24 + 0.3x 143 - 80 - 24 = 0.3x + x 1.3x = 39 ====> x = = 30. Answer. He spent $30 for repairs.