10 plus 40 plus 20 equals what?
In this question, we need to add three different numbers together. They’re all multiples of 10: 10, 40, and 20. It doesn’t matter which order we have these numbers together. They’ll always make the same total. So let’s look at a couple of ways we could find the answer. One way we could find the total is just to add the numbers in the order that they’re written. 10 plus 40 equals 50. Now, we just need to add 20. 50 plus 20 equals 70.
Let’s check our answer is correct. This time we’ll add the numbers in a different order. If we get the same answer, then it’s a sign that we’ve added correctly. Perhaps, this time, we could start by adding the two largest numbers. What’s 40 plus 20? Well, four plus two equals six. So 40 plus 20 equals 60. Finally, we just need to add 10. 10 plus 60 or 60 plus 10 equals 70. And so, we know one ten plus four tens plus another two tens equals seven tens.
10 plus 40 plus 20 equals 70.