# CAT Practice : Percents, Profits

Number of Balls

## Number of Balls

Q.23: A bucket has ‘a’ number of small and large balls out of which b% are black. Of the small balls, c% are black and of large balls, d% are black. Find the number of small balls in the bucket.
1. $a * \frac{(b-d)}{c+b-d}$
2. $a * \frac{(b-d)}{c+b-2d}$
3. $a * \frac{(c-b)}{b-d}$
4. $a * \frac{(b-d)}{c-d}$

Choice D. $a * \frac{(b-d)}{c-d}$

## Detailed Solution

Let the number of small and large balls be S and L respectively

= ) a = S + L………………..(1)

Also, b% of a = c% of S + d% of L

= ) ba = cS + dL

= ) ba = cS + d(a - S) (Putting L = a – S from (1))

= )( b – d) * a = (c – d) * S

= ) S = $a * \frac{(b-d)}{c-d}$

Correct Answer: $a * \frac{(b-d)}{c-d}$

## Our Online Course, Now on Google Playstore!

### Fully Functional Course on Mobile

All features of the online course, including the classes, discussion board, quizes and more, on a mobile platform.

### Cache Content for Offline Viewing

Download videos onto your mobile so you can learn on the fly, even when the network gets choppy!

## More questions from Averages, Ratios, Mixtures

A number of beautiful questions from three allied topics. Most sportsmen will tell you - If you know the percentage play, you can profit well from it,