Addition and subtraction

Add tens to tens and ones to ones. Exchange 10 ones for one ten; 10 tens make one hundred.

For example, 47 + 68 = 40 + 60 + 7 + 8 = 100 + 15 = 115.

If one addend changes and the other stays the same, the sum changes by the same amount in the same direction.

“Altogether” means adding both children’s stickers. Add Matas’s number of stickers to Lina’s number.

You can add the tens and ones separately. Check that you included both children’s amounts.

Count the rows and the counters in one row. Add one to the number of rows, then multiply by the counters per row.

Look for two addends whose ones add up to 10. Add this pair first, then add the remaining number.

The expression contains addition or subtraction together with multiplication. According to the order of operations, multiplication is completed first.

1. First multiply the two numbers joined by the × sign.
2. Add the product to the first number or subtract it from the first number, according to the sign shown.
3. Check that you did not simply calculate from left to right before completing the multiplication.

Rule: multiplication is completed before addition and subtraction.

Changing the order of the factors does not change the product. Find the other factor.

Look at the operation sign. For +, add the numbers; for −, subtract the second number from the first.

It can help to split the second number into tens and ones. For example, 27 − 13 = 27 − 10 − 3 = 14. When adding, you can also add the tens first and then the ones.

Changing the order of the addends does not change the sum. Both sides must contain the same addends.

Taking books away leaves fewer books on the shelf. Subtract the number taken from the starting number.

Check: the books left plus the books taken must equal the starting amount.