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Addition and Subtraction
Objectives
To add and subtract 20, 30, 40, 50 to or from 2-digit numbers using the beaded line.
Resources
📄 Choose your own | 📄 0-100 beaded line | 0-100 bead string
Vocabulary
add | subtract
Today's Lesson
Introduction
Ask your student to show 56 on the 0-100 bead string. Then ask them to show 10 more (66). Then to show 10 more than that (76). And 10 more (86).
Ask: ‘How much have we added on altogether? (30) What number sentence could we write?’
Record 56 + 30 = 86.
If it helps, remind them how Spider counts in 10s. They are doing Spider counting on the bead string!
Notice that the 1s digit doesn’t change.
Ask your student to show 45 and say that we will add 30. Discuss how to add 10, 10 and 10 again, using counting on in 10s to help (count on to add 1 number to another – we don’t know where we’ll finish).
Show how to record adding 30 to 45 on a 📄 0-100 beaded line, drawing 3 hops from 45 to 55, from 55 to 65 and from 65 to 75.
Label each hop ‘+10’, and label 75.
Record 45 + 30 = 75.
Say: ‘Show me 51. Demonstrate how we can subtract 30 by counting back in 10s.’
Record 51 – 30 = 21.
Repeat adding and subtracting 30, 40 and 50 to other 2-digit numbers by counting on or back in 10s (make sure all answers are less than 100).
This video demonstrates jumping forward and backwards in 10s along the number line, to help show how to add and subtract multiples of 10.
Main Activity
Give your student the 📄 Choose your own sheet.
Ask your student to choose a number from the yellow set. They should write their number down.
Now they choose a number from the white set and write an addition, adding the second number to their first choice.
They should draw the hops of +10 on the beaded line to help them solve it.
Ask your student now to choose a number from the blue set and write it down.
Then choose a number from the white set. They should then write a subtraction. They draw the hops of -10 on a beaded line to help them solve it.
Continue like this several more times until your student is confident with the activity, with your student writing an addition and then a subtraction.