Duratan

thanks mathematic

no this is not homework, It's just a puzzle I came across and couldn't figure it out, I dont think that is right, I think your doing the probability that there is a 1 in 11 then one in 10... that doesn't fit this scenario where we want the number of permutations of an eleven digit binary sequence that contains four 1s (the answer will be that divided by 2048)

they found out that when a cell divides it cuts of three codons on one of the dna strands this is thought to be one of the causes of aging it only happens on one DNA strand per division because the other side has an enzyme called telemorase which preserves the other DNA strand. When I was in undergrad my professor said when he was in undergrad scientists studying this used to say they are about 5 years away from stopping the aging process, when my professor said this he also said currently they say that they are about 5 years away from this being possible. Currently the scientist studying they say they are 10-15 years away from this being possible, the problem seems to be when you put telemorase on both sides of DNA it significantly increases risk of cancer. Fun thing to note if you are a fan of the mass effect series it explains that the reason the alien race, "Asari" live for about a thousand years is that they are born with telemorase on both sides of there DNA.

So I was confused if I should post this to math or to brain teasers, if I posted in the wrong spot I apologize, I got this probability question and I couldn't figure out the answer could some help me with the needed formula to solve it. The question is: given a binary string that contains 11 digits what is the probability that there is exactly four 1s in the number. I can solve half of it, I know that 11 digits means 2^11 or 2048 total numbers, but I can't figure out how to find out how many contain exactly four 1s through a formula.