Posted by **please help me out!!** on Tuesday, April 2, 2013 at 4:06am.

A bag contains 150 balls numbered 1 through 150. Three balls are drawn and placed on the table. The probability that the balls were drawn in increasing order can be expressed as a/b where a and b are coprime positive integers. What is the value of a+b?

- PROBAbility!!!! -
**Reiny**, Tuesday, April 2, 2013 at 8:55am
number of ways to draw 3 balls from 150

= 150x149x148 = 3307800

But these include triplets of the form

ABC

ACB

BAC

BCA

CAB

CBA , that is , containing the same three numbers.

Only one of these 6 would have them in the correct increasing order ,so we divide 3307800 by 6 to get 551300

so the prob of your event = 551300/3307800

= 1/6

so a/b = 1/6, and a+b = 7

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