Each row begins and ends with 1. Each of the other numbers in each row is the sum of the two numbers above it in the previous row. If we label the rows , and the entries in each row , then entry k of row n equals the binomial coefficient . Also, row n gives the coefficients in the expansion of :
The sum of the entries in row n is . If we divide entry k in row n by , then we find the probability of getting exactly k heads when flipping a fair coin n times.