Mental Mathematics: Addition

Adding from the left

57+26

(add the tens) 50+30=80

(add the units) 7+6=13

(add the two sums) 80+13=93

Breaking Up and Bridging

47+16

(add the first number to the tens in the second number) 47+10=57

(add this sum to the units in the second number) 57+6=63

Trading Off

17+36

(add 3 to make a mulitiple of 10) 17+3=20

(subtract 3 to compensate for the 3 that was added) 36-3=33

(add the two numbers) 20+33=53

Using Compatible Numbers

r

These are numbers whose sums are easy to calculate mentally

130+50+70+20+50

130+70=200

50+50=100

100+200=300

300+20=320