How many tens are there altogether? 21 plus 42.
We can use a place value chart to help us add these two numbers together. The number 21 can be broken down into two tens, which is worth 20, and one one. And the number 42 can be broken down into four tens, which is worth 40, and two ones.
First we need to add in the ones column, one plus two, which is three. Now we need to add in the tens column. Two tens plus four tens makes six tens. There are six tens altogether.