I have this friend Bruce who turned 70 late last year. I’ve only known him about a decade, so I didn’t know him when he was raising his children. At his party, I learned that one of the primary messages to his kids was that “math is everywhere.” I definitely believe that.
I’ve been hooked on numbers ever since I realized that if you add up the digits in a long number and the total adds up to 9, the number is divisible by 9. Obviously that same number, if even, is divisible by 18. If it ends with a 5, is divisible by 45, and if it ends with a zero, is divisible by 90. My daughter thinks multiplying by 9 is cool too. You multiply by 10, then subtract the number you multiplied by. So 7X9=7X10-7X1=70-7=63.
I was also fascinated that 5X5=25 and 6X4=24, 6X6=36 and 7X5=35, et al. Thus Y squared =(Y+1) (Y-1) +1. So I know if 123 squared=15129, then I know that 124×122=15128. My daughter is starting to figure this out, too.
Speaking of The Daughter, this problem in her third grade math homework really bugged me. Continue reading “M is for Math is all around”