A sum of Rs 800 is in the form of denominations of Rs 10 and Rs 20.
Question:

A sum of Rs 800 is in the form of denominations of Rs 10 and Rs 20. If the total number of notes be 50, find the number of notes of each type.

Solution:

Let the number of Rs. 10 notes be $\mathrm{x}$.

Therefore, the number of Rs. 20 notes will be $(50-\mathrm{x})$.

Value of Rs. 10 notes $=10 \mathrm{x}$

Value of Rs. 20 notes $=20(50-\mathrm{x})$

According to the question,

$10 \mathrm{x}+20(50-\mathrm{x})=800$

or $10 \mathrm{x}+1000-20 \mathrm{x}=800$

or $10 \mathrm{x}=1000-800$

or $\mathrm{x}=\frac{200}{10}=20$

$\therefore$ Number of Rs. 10 notes $=20$

Number of Rs. 20 notes $=(50-20)=30$.