Posted by **Ryan** on Wednesday, September 30, 2009 at 9:59pm.

If a number is selected at random from the set of all five digit numbers in which the sum of the digits is equal to 43, compute the probaility that this number is divisible by 11.

- Pre-Calc (ugent!!!) -
**seth**, Wednesday, September 30, 2009 at 10:07pm
haha is this a last minute calendar problem by any chance? because it's october tomorrow and i have have this problem too! lets hope somebody answers soon...

- Pre-Calc (ugent!!!) -
**MathMate**, Wednesday, September 30, 2009 at 10:11pm
The digit combinations of a 5-digit number having a sum of 43 is quite limited.

The digits are 99997, 99988.

99997 can place the 7 in 5 positions, so the number of outcomes using 4-9's and a 7 is 5.

Using 3-9's and 2-8's has 5!/(3!2!)=10 ways of arranging the numbers.

Of these, only 98989, 97999 and 99979 are divisible by 11.

Can you continue?

Check my thinking.

- Pre-Calc (ugent!!!) -
**Ryan**, Thursday, October 1, 2009 at 6:36pm
Yes seth it is

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