Question

totle cost pf 6 books and 7 pen is 79 rs and the total cost of 7 books and 5 pens is 77 rs find the cost of 1 book and 2 pens

Answer 1

Heya user,

Consider the price of Book --> 'x'
---------> The price of Pen --> 'y'

Then, cost of 6 books = 6x; cost of 7 pen = 7y

Acc. to question,
----------->   6x + 7y = Rs. 79 <--- (1)

Again, similarly, we get: 7x + 5y = Rs. 77 <-- (2)

Now, Equation (1) => 6x + 7y = 79 => 42x + 49y = 553 [ multiply with 7 ]
Similarly, Eqn. (2) => 7x + 5y = 77 => 42x + 30y = 462 [ multiply with 6 ]

Now, Eqn (1) - Eqn (2) gives --->
-------> 19y = 91 => y = 91/19 = 4.8 (approx)

Putting this value in either eqn. --> 6x + 7*4.8 = 79 => x = [ 79 - 33.6 ] / 6
=> x = 45.4 / 6 = 7.56 [ approx ] 

Hence, Cost of one book = Rs. 7.56 ( approx )
Cost of two pen = Rs. 4.8 * 2 = Rs. 9.6 ( approx ) ..

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For exact values,


Consider the price of Book --> 'x'
---------> The price of Pen --> 'y'

Then, cost of 6 books = 6x; cost of 7 pen = 7y

Acc. to question,
----------->   6x + 7y = Rs. 79 <--- (1)

Again, similarly, we get: 7x + 5y = Rs. 77 <-- (2)

Now, Equation (1) => 6x + 7y = 79 => 42x + 49y = 553 [ multiply with 7 ]
Similarly, Eqn. (2) => 7x + 5y = 77 => 42x + 30y = 462 [ multiply with 6 ]

Now, Eqn (1) - Eqn (2) gives --->
-------> 19y = 91 => y = 91/19

Putting this value in either eqn. --> 6x + 7*91/19 = 79
=> x = [ 79 - 637/19 ] / 6
=> x = [ 1501 - 637 ] / 19 / 6 = Rs. 864/(19*6) = Rs. 144/19
Hence, Cost of one book = Rs. 144/19
Cost of two pen = Rs. 91/19 * 2 = Rs. 182/19

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