Let the c.p of one ball be Rs x
c.p of 17 balls=17x
c.p of 5 balls=5x
s.p of one ball=Rs 20
s.p of 17 balls=20*17=340
On selling 17 balls at Rs.20 there is a loss equal to cost price of 5 balls
c.p of 17 balls - s.p of 17 balls = c.p of 5 balls
Let us assume that the cost price of one ball be Rs x.
The cost price of 17 balls would be Rs 17x and it is mentioned that there is a loss:-
Loss = Cost Price - Selling Price = Rs (17x - 720).
It is also said that this loss is equal to the cost price of 5 balls so next step is to calculate the cost price of 5 balls which would be Rs 5x only.
In mathematical form,
17x - 720 = 5x, then 17x - 5x = 720, then 12x = 720, then x = 720/12
x = 60 . And we assumed x to be the cost price of one ball which is Rs. 60.
Actually it was of only three steps but i tried to explain in a lucid manner.
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