Let the number of 10Rs notes be x
Number of 20Rs notes be 50 – x
Amount due to 10Rs notes = 10 × x = 10x
Amount due to 20Rs notes = 20 × (50 – x) = 1000 – 20x
So the total amount is Rs 800
10x + 1000 – 20x = 800
-10x = 800 – 1000
-10x = -200
x = -200/-10
= 20
∴ The number of 10Rs notes is 20
Number of 20Rs notes are 50 – 20 = 30