Near Doubles

Some facts sit right next door to a double. 7 + 8 is almost 7 + 7.

Use the double, then adjust

7 + 7 is 14. The 8 is one more than 7, so the answer is one more than 14.

So 7 + 8 = 15. You never counted. You used a fact you already had.

Either neighbour works

You could also use 8 + 8 = 16 and take one away. Both roads reach 15.

What makes two numbers near doubles

Two numbers are near doubles when they are one apart, like 6 and 7, or two apart, like 6 and 8. You do not add them from scratch. You find the double hiding inside them, then fix the difference. For 6 + 7, the double is 6 + 6 = 12, and 7 is one more than 6, so the answer is one more: 13.

Two doubles to choose from

For 6 + 7 you could use the double of 6 and add one, or use the double of 7 and take one away: 7 + 7 = 14, then 14 - 1 = 13. Both routes land on 13. Pick whichever double you know better. Getting the same answer two ways is good evidence you are right.

The slip to watch for

The common mistake is adjusting in the wrong direction — using 6 + 6 = 12 and then taking one away instead of adding one. Guard against it by asking whether the answer should be bigger or smaller than the double before you calculate. 6 + 7 has more in it than 6 + 6, so the answer must be bigger. That check takes a second and catches the error every time.