Remember if the units add up to 10 or more you will have to exchange the ten into the tens column.
Formal subtraction of Tens and Units
Always check the units column; if there are not enough units on the top line you will need to exchange a ten for 10 units. Make sure you always show your working out.
Multiplying Tens and Units
Always start to multiply at the units. Don't forget if the answer in the units is 10 or more you will have to exchange. Then you multiply the tens and add the extra ten. Be careful to multiply carefully.