(In reply to without a calculator
It turns out that a number with 49 as its last two digits can be a perfect square only if the hundreds digit is even. This has probability 1/2 of happening. However, if it is even, the probability that is a square is 8 times what it otherwise would be, leaving us with just the same probability of four times the most naive estimate, i.e., it is still 1/1,250,000,000.
Posted by Charlie
on 2004-03-23 14:57:04