Question

Mohan purchase 6 black and X white balls. The price of black ball is 5/2 of the price of white ball. At the time of making the bill clerk made a mistake and interchanged the number of balls, due to this the bill amount increased by 45%. Find x.
1. 25
2. 15
3. 10
4. 18

Answer 1

Correct Answer - Option 2 : 15

Given:

Mohan purchase 6 black and X white balls. The price of black ball is 5/2 of the price of white ball. At the time of making the bill clerk made a mistake and interchanged the number of balls, due to this the bill amount increased by 45%. 

Concept used:

Percentage

Calculation:

Number of black balls = 6

Number of white balls = x

Price of black balls = (5/2) × Price of white balls.

Original bill = 6 × 5 + 2 × x = 30 + 2x

At the time of making the bill clerk made a mistake and interchanged the number of balls, 

Now, number of black balls = x & number of white balls = 6

Wrong bill = 5x + 12

As per the question, 

⇒ \(\frac{{30 + 2x}}{{5x + 12}} = \frac{{100}}{{145}} = \frac{{20}}{{29}}\)

⇒ 870 + 58x = 100x + 240

→ 630 = 42x

∴ x = 15