Commutative number sentences I

This task is about missing numbers that make number sentences true.

Question 1Change answer

a)  Find the missing number in each number sentence and write it in the box.
     i)      7 + 6 = 6 + 
 
     ii)    23 +   = 46 + 23
 
     iii)      + 67 = 67 + 75
 
     iv)    87 + 79 =   + 87

Question 1Change answer

b)  All the number sentences below are true. 
     Explain how you know they are true without having to add up the numbers.
 
45 + 63 = 63 + 45
 
189 + 52 = 52 + 189
 
364 + 817 = 817 + 364
 
2,579 + 168 = 168 + 2,579