ACTIVITY 7

Example: Study number sentence: 9 – 2 = We are not going to draw any pictures to solve this number sentence. Use mental maths and decide on an answer. You will then see – by using inspection – that the answer is 7.

1. Solve the number sentences using inspection.

1.1 1.2 1.3 1.4 1.5

Question

273 + 6 = 62 + 5 = 997 – 33 = 42 – 12 = 54 – 12 =

Answer 279 67 964 30 42

Now let us look at the solving of number sentences through the trial and improvement method.

Using this method, you will guess an answer, but you will write it down and then calculate the number sentence. If your answer is not correct, you can try another answer and calculate the number sentence until it is correct or until the number sentence is TRUE.

This number sentence is FALSE:

413 – 2 = 410

This number sentence is TRUE:

413 – 2 = 411

Example: Study the number sentence below and use the trial and improvement method to solve it.

156 – = 149

Attempt 1: Guess an answer that will make the number sentence TRUE. Guess that a 6 in the block will make the number sentence true.