Playdates

Playdate focus

Use 10 as an intermediate stop to make mental arithmetic for adding and subtracting a lot easier, as well as reinforcing number relationships.

Storybook properties

This has skip counting and number properties.

Activities properties

These involve adding, subtracting, and number bonds.

Number bonds for 10

The number 10 is often a handy mental arithmetic midway point to use for doing addition and subtraction problems that involve numbers above 10. Your child should have a strong command of the number bonds for 10 to take full advantage of these methods.

Addition sums over 10

Suppose your child is given the addition problem 5 + 7. The number bond for 10 using 7 is 3, so your child can use 3 of the 5 to get to 10. The remaining 2 of the 5 will bring the total to 12. The point was to break up the 5 into two pieces, 3 and 2 – one which got the 7 to 10, and the other gets added onto the 10. This problem could also have been done the other way. The 7 could have been broken up into 5 and 2 – the 5 would be added to the original 5 to get 10, and then the 2 would be added to 10 to get 12.

Notice that this is similar to the thinking for doing addition compensation.

Subtracting from a number bigger than 10

Let’s use 12 – 7 as our example. We can do this as a take away or a difference problem.

As a take away problem, we’ll use 2 of the 7 to get 12 down to 10. We then have 5 of the 7 left to take the 10 down to 5. We broke 7 into 2 and 5 to be able to use 10 as an intermediate stop along the way.

As a difference problem, the total distance between 12 and 7 is the distance between 12 and 10 plus the distance between 10 and 7. The distance between 12 and 10 is 2, and the distance from 10 and 7 is 3, so the total distance is 2 plus 3, which is 5.