Step 1: Identify the articles
We Identify two articles
1. Book
2. Pen
Step 2: Assign variables to the articles
Book = x
Pen = y
Step 3: Deduce the problem into equations
Five books and seven pens together cost Rs 79 ----> 5x +7y = 79
seven books and five books together costs Rs77 ----> 7x +5y = 77
Step 4: Find one variable by eliminating the other
Equation 1 5x +7y = 79
Equation 2 7x +5y = 77
Multiply Equation 1 with coefficient of x from Equation 2
( 5x +7y = 79 ) * 7
35x + 49y = 553
Multiply Equation 2 with coefficient of x from Equation 1
( 7x +5y = 77 ) * 5
35x +25y = 385
Step 5: Subtract the two new Equations
35x + 49y = 553 - (35x +25y = 385)
(35 - 35)x + (49 - 25)y = (553 - 385)
24y = 168
y = 168 / 24
y = 7
So we can say that each Pen cost Rs 7
Step 6: Substitute the value of y in Equation 1 to Find x
5x +7y = 79
5x + 7(7) = 79
5x +49 = 79
5x = 79 - 49
5x = 30
x = 30/5
x = 6
So we can say that each Book cost Rs 6
Now we need to find cost for cost of one book and two pens
6 + 2(7) = 6 +14 = 20
Cost ofone book and two pens is Rs 20
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