[math-fun] reciprocal mod 100

Q: What's the reciprocal of 33 mod 100? Hint: Add 64. When N ends in 3, the (mod 100) reciprocal of N is N+64. So the reciprocal of 33 is 97. 33*97 = 3201 = 1 (mod 100). The whole algorithm ... Suppose the tens digit of N is T. If N = 10T+1, then 1/N = 102-N 10T+3, N+64 10T+7, N+36 10T+9, 98-N Rich