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Adding Two Digit Numbers
Objectives
To calculate simple additions, and to be able to simplify the calculation if we are able to do so.
Resources
Abacus 4 Textbook 1 | Squared paper
Today's Lesson
Main Activity
Ask your student to recite two times tables and to answer questions on these as the mental warm up.
Turn to page 20 in Abacus 4 Textbook 1.
Watch the ‘Adding 2 digit numbers using partitioning’ video.
Look at the addition calculations. Remind your student of the earlier pages in the book, where it is unnecessary to include the zeros if you are just working with tens or hundreds. For example, 42 + 23 in the expanded method would require your student to write out the calculation in this way:
40 + 20 = 60
2 + 3 = 5
(Answer: 42 + 23 = 65)
We have understood previously that it is not necessary to write the zero down if the two numbers we are working with both end in one zero. So we could simply add
4 (tens) + 2 (tens) = 6 (tens)
2 + 3 = 5
(Answer 42 + 23 = 6 tens + 5 = 65)
We know the 6 represents 60, because of its place. Ask your student to copy and complete the calculations on the page. Remind them to take care if the answer when adding the ones comes to more than 9, as there must be another 1 added to the tens answer for the carry forward.
For example:
47 + 78 =
Partition the numbers into tens and ones so we have:
40 + 70 = 110
7 + 8 = 15
15 is larger than 9, and has 1 ten which we need to add to the tens column of our first number:
110 + 10 = 120
Then add the ones:
120 + 5 = 125
Complete Q1 – 16 using partitioning.
Now look at the ‘Think’ activity. Ask your student to tell you what calculations they need to do for Q17 and Q18. Remind your student that the problems require a sentence answer, as well as the calculation.