Odd and even in addition worksheet

Part A: Working out and filling in

1. 1. 6

   Adding 8 has to give an even number. Is 8 odd or even, so which kind must the number be?

   To give an even sum with 8, a number must be odd if 8 is odd and even if 8 is even: from 19 to 30 there are 6 of them.

2. 2. 2

   Adding 4 has to give an even number. Is 4 odd or even, so which kind must the number be?

   To give an even sum with 4, a number must be odd if 4 is odd and even if 4 is even: from 5 to 9 there are 2 of them.

3. 3. 4

   Adding 3 has to give an even number. Is 3 odd or even, so which kind must the number be?

   To give an even sum with 3, a number must be odd if 3 is odd and even if 3 is even: from 16 to 23 there are 4 of them.

Part B: Choose, or true or false

1. 4. True

   First see whether 20 and 8 are each odd or even, then think what kind their sum must be.

   20 + 8 = 28. Or just look at whether each is odd or even: odd + odd and even + even are even, odd + even is odd.

2. 5. D. 22

   Look only at each number's ones digit: 0, 2, 4, 6 and 8 are even.

   A number ending in 0, 2, 4, 6 or 8 is even: 22 ends in an even digit, so 22 is even.

3. 6. False

   First see whether 17 and 6 are each odd or even, then think what kind their sum must be.

   17 + 6 = 23. Or just look at whether each is odd or even: odd + odd and even + even are even, odd + even is odd.

4. 7. True

   No need to add: just look at the ones digits of 304 and 695. Is each odd or even?

   Look at the ones digits only: odd plus even is odd; two odds or two evens make an even number. 304 + 695 = 999.

5. 8. B. 261 + 370

   Look only at the ones digits in each sum: what do odd + even, odd + odd and even + even give?

   261 ends in an odd digit and 370 in an even one: odd + even = odd.

6. 9. True

   No need to add: just look at the ones digits of 476 and 803. Is each odd or even?

   Look at the ones digits only: odd plus even is odd; two odds or two evens make an even number. 476 + 803 = 1279.

7. 10. False

   No need to add: just look at the ones digits of 442 and 232. Is each odd or even?

   Look at the ones digits only: odd plus even is odd; two odds or two evens make an even number. 442 + 232 = 674.

8. 11. True

   First decide whether 23 + 64 is odd or even, then add on 90.

   First see whether the first two make odd or even, then add the third: 23 + 64 + 90 = 177.

9. 12. False

   First decide whether 77 + 38 is odd or even, then add on 51.

   First see whether the first two make odd or even, then add the third: 77 + 38 + 51 = 166.

Part C: Word problems

Marking: 2 for the working, 1 for the answer, 1 for the sentence.

1. 13. 0 people

   First see whether each group has an odd or even number of people. Is the total odd or even?

   22 people in all: an even number pairs up exactly, an odd number leaves 1. Or just look at whether each group is odd or even.

2. 14. 275

   The odd house numbers go up by 2 each house. 3 houses further on, how much more is that?

   Odd numbers go up by 2 a house: 3 houses on is 3 lots of 2 more, number 275 (odd + even = odd).

3. 15. 2 ways

   The total must be even. Ka-yan shows 2. Does May need the same kind of number as 2 (odd or even), or the other kind?

   For an even total, May's number must be odd if 2 is odd and even if it is even: 2 of 1 to 5 are.

4. 16. 9 bags

   First work out how many there are, then put them in twos. If the total is odd, what about the one left?

   17 in all, two to a bag: an odd total needs one more bag for the one left over, so 9 bags.

5. 17. 3 ways

   The total must be even. Tsz-hin shows 3. Does Ka-yee need the same kind of number as 3 (odd or even), or the other kind?

   For an even total, Ka-yee's number must be odd if 3 is odd and even if it is even: 3 of 1 to 5 are.

6. 18. 11 bags

   First work out how many there are, then put them in twos. If the total is odd, what about the one left?

   21 in all, two to a bag: an odd total needs one more bag for the one left over, so 11 bags.