Look at how Benjamin added 32 to 27 by adding three tens and then two ones. Use number lines to find the answers to these sums, 43 plus 32, and then 67 plus 14.
Before we calculate the answer to those sums, let’s go back and look at how Benjamin has used the number line to help him find the answer to his addition. Benjamin is adding 32 to 27. This means that he starts with the number 27, and then adds 32 onto it. This is why his number line begins with the number 27.
Instead of adding 32 all in one go, Benjamin partitions the number 32 into tens and ones. We can split 32 into 30 and two, which is the same as adding three tens and two ones. And that’s why these are the jumps that Benjamin makes on his number line. First, he adds three tens. So, he starts at 27 and counts on in tens three times, 37, 47. And then, from 57, he adds two ones, 58, 59. So, that’s how he arrives at the answer 59.
Let’s use number lines in a similar way to find the answers to the sums. Firstly, 43 plus 32. We start with the number 43. And then, we need to partition 32 into tens and ones. 32 is three tens and two ones, as we’ve seen already. So, we need to make three jumps of 10 and two jumps of one. Let’s count in tens from 43, 43, 53, 63, and 73. Now let’s add the two ones, starting with 73, 74, 75. And so, by adding three tens and two ones, we found that 43 plus 32 equals 75.
Let’s use the same method to calculate 67 plus 14. Start with the number 67. Partition the number 14 into one ten and four ones. Count on one ten, 67, 77. And then, add our four ones, 78, 79, 80, and 81. And so, by adding one ten and four ones, we found that 67 plus 14 equals 81.