the price of 4 books and 10 pens is ₹ 100 and the price of 7 books and 9 pens cost ₹ 158 , then find the cost of 2 books and 5 pens.
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let book = x and pen = y
then
(4x+10y=100)*9
(7x+9y=158)*10
36x+90y=900
70x+90y=1580
36x+90y=900
-_____________
34x=680
x=20
and for y
4*20+10y=100
80+10y=100
10y=20
y=2
so the cost of 2 books is 2*20=40 rs
and the cost of 5 pens is 5*2=10 rs
total cost is 40+10 = 50
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