MSC #14 – Digit Sums: Casting Out 9s December 14, 2019 Ike Prudente 30 Master Strategies in Computing, Math Education All grade-school learners are taught that “a number is divisible by 9 if the sum of its digits is divisible by 9”. However, only a few are taught that there is no need to divide. If the digit sum has… Read More→