수학 트릭(암산 연습) (100+) PRO

수학 트릭:

x + y

x - y

x * y

x / y

x * 11

x * x

x = 15, 25, 35, 45, 55, 65 ..

x * 5

x * 9

x * 4

x / 5

1000 - x

x * y

y = 2, 4, 8

2 ^ x

x + y

y = 91 ~ 109, 191 ~ 209, 291 ~ 309 ..

x - y

y = 91 ~ 109, 191 ~ 209, 291 ~ 309 ..

x * y

x,y = 10 ~ 19

x * x

x = 11 ~ 99

x1x2 * y1y2

x1 = y1 = 1 ~ 9, x2 + y2 = 10

23 * 27, 59 * 51, 37 * 33, 68 * 62 ..

x * x

x = 50 ~ 59

x * x

x = 40 ~ 49

x * y

x,y = 11, 21, 31, 41, 51, 61, 71, 81, 91

x% -> y

x * x

x = 100 ~ 109