Melody

good spotting Catmg    

7!/(3!*2!*2!)

I think   4/9

the last digit can be 2,4,6,8,    1,3,5,7,9   It cannot be 0 because the first digit cannot be 0

Thanks Heureka,  

I did not read the question properly.   I didn't notice that it was only odd values of r.

99C0+99C99=1+1=2

99C1+99C98=99+99 = 198

99C2+99C97=4851+4851=9792

If I add all those together I get   9900

So the sum is  2^99 - 9900

I think it is anyway.

The discriminant in the quadratic formula must equal 0

\(\triangle=0\\ b^2-4ac=0\\ 400-28a=0\\ 400=28a\\ a=14\frac{2}{7}\)

Thanks for your response.   

I have opened the original thread.

If you do not like my answer then state why in a new post on the original thread.

Oh since it is back a bit, I might not see it.  Post here a little message saying you have done so.

I get 150, see if that works.

Try 48 and tell us if that is accepted.....