What are tidy numbers?

1+9=10
2+8=10
3+7=10
4+6=10
5+5=10

To work out  7+5 try  7+3=100
then add 2 more

To work out  12-8 try 12-2=10

then take 6 more off the 10 i.e 10-6=4


This way we can stop counting on or backwards on our fingers.

Harder problems can be done this way also eg 23-7.  Take 3 off the 23 then you have come down to a tidy number of 20.
You now need only take 4 more off. 10+6+4 =20

Let's try 14+8. We know that 6+4=10,

so 14+6=20 then add 2 more to get 22

LOOK for tidy numbers.