Explain how making a 10 can help you find the sum of 9+8

The arithmetic pattern of adding 10 to a number will help us find the sum of 9+8.

We know that 4+10 is 14, 6+10 is 16 or 2+10 is 12. You can always add 9 to something by adding 10 to the number (instead of 9) and then counting down one (since 9 is one less than 10). For example: to find 9+8, add 10+8 (10 instead of 9), which is 18, and then count down one to get 17.

The same pattern goes with adding 8 to a number, you can add 10, and then count down two numbers. So, to find the sum of 9+8, add 9+10 which is 19, and then counting down two numbers, the answer is 17.

Find out why young kids are struggling with Common Core math at the Washington Post.

Monday, November 25 2013

Source: http://olc.spsd.sk.ca/de/math1-3/p-mentalmath.html

Related questions