Question

A bag contains 5 white, 3 yellow and 2 green balls all identical except the color. A ball is drawn and set aside , a second ball is drawn . what is the probality that the balls are of different colours

Answer 1

Answer:

5/8) * (4/7) + ( 3/8)* (2/7) = 13/28

The explanation for my answer could go a bit longer but it’s pretty easy to understand the concept & a good approach to hit such questions right in few seconds. Hope it helps !!!!!!

(Remember: we always multiply for AND case & do addition for OR case)

Selection would be in 2 ways possible i.e ( WHITE AND WHITE ball “OR” BLACK AND BLACK ball ) because we have been asked to choose two balls of same color. You cant pick White & White AND Black & Black because in this way u ll end up picking 4 balls which is wrong. so we used “OR”

Now,,,,,Think it like , what is the probability of getting 1 white ball on your first selection out of all balls….???

(Most imp approach)- Don’t consider both selection only in one go !!! so just think it one by one. …..O.K!

Hopefully u too thought it = 5/8 ( i.e there are 5 white balls and you selected one from total 8 balls) ……………………………………….GOOD :)

Now, what about the next ball being white…………..is the most common mistake many could do.

Problem is we have 5 white balls & we have chosen 1 ball out from that,,,, Right?

So, there are only 7 balls left for next selection & How many are there white balls left to select now??? = 4 ( because we have already selected one, out from 5)….. :)

2. PROBABILITY OF GETTING WHITE BALL AGAIN IN SECOND CHANCE = 4/7

PROBABILITY OF GETTING BOTH WHITE = (5/8) * (4/7) (remember, getting the first ball changes the probability of another, since we wanted a white AND a white ball so we ll multiply them both )

3. Similarly, for black we have 2 scenarios, hopefully u thought =(3/8)

4. Can u tell me probability of getting another black now???? = (2/7) ( LIKE WE DID FOR WHITE BALLS)

ANSWER……Probability of getting white & white OR black & black =

= (5/8) * (4/7) + ( 3/8)* (2/7) = 13/28 (& - multiply, OR -addition )

Hope, my long explanation helped you to understand the easy approach for such questions. :)

Thanks for reading! :) have a good day :)