# On selling a pen 5% loss and a book at 15% gain A gains 7rs if he sells the pen at 5% gain and the book at 10% gain then he gains 13rs the actual price of the book is?

1
by ekalavyaachanta

2015-04-09T20:11:15+05:30

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Let the cost of a pen be : Rs P.
let the cost of a book be Rs B.

Loss on selling the pen:  Rs  P * 5/100
Profit on selling the book : Rs  B * 15/100

The overall gain =  15 B/100 -  5 P /100 = Rs 7
3 B - P = 140        ---(1)

gain on selling pen : 5 /100 * P
gain on selling book:  10/100 * B
total gain =  5/100 * P + 10/100 *  B =  13
P + 2 B = 260    -- (2)

add the two equations above: to get:    5 B = 400
Price of book = Rs 80
So price of pen =  3 B - 140 =  Rs 100.  by using (1) above.

200% of X is same as 2 * X.
profit = profit % * investment = 5% * I = 5/100 * I = I/20. Revenue = investment + profit = investment + investment * profit%. So Revenue = investment + 5/100 * investment = investment [ 1 + 5/100. So reveneue = investment * 105/100 = 1.05 investment.
loss = loss % * investment. revenue = investment - loss = investment - investment * loss% Hence, revenue = investment - investment * 5/100 = investment [1 - 5/100] = investment * 95/100 = 0.95 * Investment
profit => revenue > investment. Loss means revenue < investment.
So we can directly write: Let 22% profit occur, then Revenue = 1.22 * Investment. If 31% loss occurs, then revenue = 0.69 * investment.