Ex 3.4, 2
Form the pair of linear equations in the following problems, and find their solutions (if they exist) by the elimination method :
(iv) Meena went to a bank to withdraw Rs 2000. She asked the cashier to give her Rs 50 and Rs 100 notes only. Meena got 25 notes in all. Find how many notes of Rs 50 and Rs 100 she received.
Let Number of Rs. 50 notes = x
& Number of Rs. 100 notes = y
Given that
Total notes is 25
(Number of Rs 50 notes) + (Number of Rs 100 notes) = 25
x + y = 25
Also, given that
Total amount withdrawn = 2000
Thus,
50x + 100y = 2000
50 (x + 2y) = 2000
x + 2y = 2000/50
x + 2y = 40
Hence, our equations are
x + y = 25 …(1)
x + 2y = 40 …(2)
Using elimination method
−y = −15
y = 15
Putting y = 15 in equation (1)
x + y = 25
x + 15 = 25
x = 25 – 15
x = 10
So, x = 10 & y = 15 are the solution of our equations
Therefore,
Number of Rs 50 notes = x = 10
Number of Rs 100 notes = y = 15

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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