Question

The average cost of 5 books and 4 pens is 36.The average cost of 7 books and 8 pens is 48.Find the cost of 12 books and 12 pens together

Answer 1

Answer:

96

Step-by-step explanation:

suppose cost of book =x

soppose cost of pen. =y

if cost of 5 book and 4 pen = 36

therefore 5x+3y=36-------(1)

if cost of 7 book and 8 pens= 48

therefore 7x+3y=48-------(2)

eq (1)×7 and eq(2)×5 and eliminate eq 1 and 2

therefore 35× + 21y = 252--(3)

35x + 15y = 240--(4)

when we subtract eq 3 and 4

we get y = 2

put the value of y in eq 1

5x+3y=36

5x+3(2)=36

5x+6=36

5x=30

× = 6

cost of 1 book =6Rs

cost of 1 pen= 2Rs

for 12 books and 12 pen

=12x+12y

=12(6)+12(2)

=72 + 24

= 96

therefore cost of 12 pen and 12 books together = 96