Mental addition

This week we are practising adding and subtracting mentally. There are several strategies that can be used.

Adding a one-digit number to a two-digit number:

Method 1. Counting on. Eg. 23 + 4 = ? Count up 4 from 23, say 24, 25, 26, 27 (don't say starting number as nothing has yet been added!)

Method 2. Adding on. Eg. 23 + 4 = ? Knowing that 3 + 4 = 7 therefore 23 + 4 = 27

Method 3. Adding on when answer goes beyond next 10. Eg. 23 + 8 = ? Add on 7 to make it up to 30 then add on 1 to make 31


Adding a two-digit number to a two-digit number:

Method 1. Adding 10s then 1s. Eg. 23 + 25 = ? First add 10s, 20 + 20 = 40, then add 1s, 3 + 5 = 8, then add together, 40 + 8 = 48

Method 2. Adding on 10s then 1s. Eg. 25 + 17 = ? Add 10 onto 25 = 35, then add on 7 using methed 3 from above.


This website lets you practise adding two-digit numbers (select level 3):
http://www.crickweb.co.uk/assets/resources/flash.php?&file=digitmenu


Practise adding one-digit and two-digit numbers at this website (select adding and medium level):
http://www.mrnussbaum.com/mayan-math/index.html