Question

A hundred rupee note was changed into ten rupee notes and twenty rupee notes. There were seven notes in all. How many of each denomination were there?

Answer 1

Total number of notes = 7

Let the number of 10 rupee notes be x.

The number of 20 rupee notes = 7 − x

Algebraic form of the problem is:

10x + 20(7 − x) = 100

⇒ 10x + 140 − 20x = 100

⇒ −10x + 140 = 100 (since 10x - 20x = -10x)

⇒ -10x = 100 − 140

⇒ -10x = -40

⇒ $x=$ $\frac{-40}{-10}=4$

Therefore, there are 4 notes of 10 rupees and 7 − 4 = 3 notes of 20 rupees.