34
Finding an unknown addend
Textbook Part 1, pp. 70–71
GoalFind the missing addend when the sum and one addend are known.
New words
unknown · noma’lumaddend · qo‘shiluvchisum · yig‘indi
Explanation
Rule: to find an unknown addend, subtract the known addend from the sum. If _ + 3 = 8, the unknown = 8 − 3 = 5. Check: 5 + 3 = 8 ✓.
Worked examples
9 children should take part in a contest. 6 girls have arrived. Boys: 9 − 6 = 3.
A ladybird crawled 3 marks to the right and reached 9. Where was it before? 9 − 3 = 6.
Class activity
Bag game: the teacher puts some blocks in a bag, then adds 2 more. “There are 7 now. How many were in the bag before?” Children work it out, then open the bag to check.
Practice
1
_ + 4 = 9
5
2
6 + _ = 10
4
3
10 sports kits were prepared for the “Fun Starts” games. 7 children have put them on. How many more children will take part?
3
4
Check: is 5 the answer to _ + 2 = 7?
Yes, 5 + 2 = 7