20. Rules and Properties


Talk About 7 + 6 + 9 =


What answer did you get? Which 2 numbers did you add first? How many different ways could you have done this sum? Would it make any difference to the final answer?


Now try this one. 15 – 7 – 6 =


What answer did you get? Discuss your answer with the people near you.


Did anyone get a different answer to you? How many possible answers are there? What are they?


1. Try these. See if they have more than 1 possible answer. If they do have more than 1 possible answer, work out each of the possibilities.


a) 9 + 5 + 12 e) 3 × 4 + 2 i) 6 × 2 × 5


m) 72 ÷ 12 – 4


b) 10 + 7 – 5 f) 7 + 5 × 3 j) 40 ÷ 5 + 3 n) 60 ÷ 6 × 2


Do the Work Inside Brackets First


To help us find the particular answer that is being looked for, brackets are sometimes placed around 1 of the operations. We always perform the operation that is inside the brackets first.


23 – 9 + 4


Possibilities: (23 – 9) + 4 =


14 + 4 = 18 Strand: Algebra


Curriculum Objectives: Explore and discuss simple properties and rules about brackets and priority of operation; identify relationships and record verbal and simple symbolic rules for number patterns.


139 23 – (9 + 4) = 23 – 13 = 10


c) 16 – 8 + 3 g) 5 × 6 – 2 k) 30 + 6 ÷ 3 o) 9 × 12 ÷ 4


d) 23 – 7 – 4 h) 14 – 3 × 3 l) 45 – 9 ÷3 p) 24 ÷ 6 ÷ 2


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