Question

5 books and 7 pens together cost Rs.79 whereas 7 books and 5 pens cost Rs77 . find the total cost of 1 book and 2 pens?

Answer 1

Let a book be 'b' and pen be 'p'
The first equation is 5b+7p=79
The second equation is 7b+5p=77
Firstly multiply equation one with 7
Secondly multiply equation two with 5
Solve the both multiplied equations then we would get p=7
Substitute in any equation and we get b=6
Now substitute 'b' value in any equation and we will get b=6
Place the given values in the expression b+2p and we will get 20
The cost of one book and 2 pens is 20 rs.

Answer 2

Solution:-
Let the cost price of 1 book be Rs. 'x' and the cost price of 1 pen be Rs. 'y' respectively.
So, according to the question.
⇒ 5x + 7y = 79  ...........(1)
⇒ 7x + 5y = 77  ...........(2)
Multiplying the equation (1) by 7 and equation (2) by 5, we get
⇒ 35x + 49y = 553.......(3)
⇒ 35x + 25y = 385.......(4)

Now, subtracting (4) from (3), we get.
⇒ 24y = 168
⇒ y = 168/24
⇒ y = 7
Substituting value of y = 7 in (1), we get.
⇒ 5x + 7*7 = 79
⇒ 5x = 79 - 49
⇒ 5x = 30
⇒ x = 6
So, cost of 1 book is Rs. 6  and cost of 1 pen is Rs. 7 
Now, cost of 1 book and 2 pens = 6 + (7*2)
= 6 + 14
= Rs.20
Answer.