Let's learn how to subtract 12 from 31. First, let's understand what 31 looks like. We can show 31 as 3 groups of ten blocks and 1 single block. Each group of ten has exactly 10 blocks. So we have 3 tens and 1 one, which makes 31.
Now, we need to take away 12 blocks. What is 12? It's 1 group of ten and 2 single blocks. So we need to take away 1 ten and 2 ones from our 31. Let's mark what we need to subtract in red.
But wait! We have a problem. We have only 1 single block, but we need to take away 2 single blocks. We don't have enough! What can we do? We need to break apart one of our groups of ten into 10 single blocks. This is called regrouping or borrowing. Let's take one group of ten and break it into 10 individual blocks.
Now we have 2 groups of ten and 11 single blocks. That's because we had 1 single block, and we added 10 more by breaking apart one group of ten. Now we can subtract. First, let's take away 2 single blocks from our 11 single blocks. 11 minus 2 equals 9 single blocks. Next, let's take away 1 group of ten from our 2 groups of ten. 2 minus 1 equals 1 group of ten. So we're left with 1 group of ten and 9 single blocks. That's 19! So 31 minus 12 equals 19.
Let's review what we learned. We started with 31, which is 3 tens and 1 one. We needed to subtract 12, which is 1 ten and 2 ones. Since we didn't have enough ones to subtract from, we had to break apart 1 ten into 10 ones. This gave us 2 tens and 11 ones. Then we subtracted 2 ones from 11 ones to get 9 ones, and 1 ten from 2 tens to get 1 ten. So our final answer is 1 ten and 9 ones, which is 19. Great job understanding subtraction with regrouping!