Answer:
Let's define:
G = cost of a goat
S = cost of a sheep.
We know that the total cost for a goat and a sheep is £120, then:
S + G = £120
And the cost of the goat is twice the price of the sheep, then:
G = 2*S
To solve this system, we can just replace the second equation into the first one, then we get:
S + (2*S) = £120
3*S = £120
S = £120/3 = £40
This means that each sheep costs £40
And the cost of a goat is:
G = 2* £40 = £80.
Now we know that he sold both of them, where:
s = price of the sheep
g = price of the goat.
We know that he sold both of them for £180, then:
s + g = £180
And the profit of the sheep is twice the profit of the goat, then:
(s - S) = 2*(g - G)
(s - £40) = 2*(g - £80)
s - £40 = 2*g - £160
Then we have a system of equations:
s + g = £180
s - £40 = 2*g - £160
To solve this, we first could isolate g in the first equation:
g = £180 - s
Replacing this in the other equation we get:
s - £40 = 2*( £180 - s) - £160
s - £40 = £360 - 2*s - £160
s - £40 = £200 - 2*s
s + 2*s = £200 - £40 = £160
3*s = £160
s = £160/3 = £53.33
Then the percentage profit for the sheep is:
percentage profit = (s/S)*100% = (£53.33/£40)*100% = 133.3%
Then the percentae profit is 33.3%, which means that the sheep was sold at 133.3% of its original cost, leaving a profit of 33.3% of its original cost.
