SOLUTION: A pet shop bought a litter of puppies for 120 pesos. All but four of them were sold, at a profit of 5 pesos each, for a total of 120 pesos. How many puppies were in the litter?
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Question 1138531: A pet shop bought a litter of puppies for 120 pesos. All but four of them were sold, at a profit of 5 pesos each, for a total of 120 pesos. How many puppies were in the litter? Answer by ikleyn(52788) (Show Source):
Let "n" be the number of puppies originally.
Then the buying price of each of n puppies was .
The selling price of each of sold (n-4) puppies was .
The profit was 5 pesos for each sold puppies, i.e.
- = 5 pesos.
It is your basic equation to find "n". To solve the equation, multiply both sides by n*(n-4).
120n - 120*(n-4) = 5n*(n-4)
120n - 120n + 480 = 5n^2 - 20n
480 = 5n^2 - 20n
5n^2 - 20n - 480 = 0
n^2 - 4n - 96 = 0
(n-12)*(n+8) = 0
The last equation has 2 roots 12 and -8, but only positive n= 12 is meaningful solution to the given problem.
ANSWER. Where were 12 puppies in the litter originally.
