AO elaboration and other teaching resources [6]

This is a level 3 number activity from the Figure It Out series. It relates to Stage 6 of the Number Framework.

solve addition problems using mental strategies

#### Activity One

This activity provides an opportunity for students to practise addition skills. The most efficient way to find the correct path is to add the ones digits only to find a number with a six in the ones place. There is only one path that gives an answer with six in the ones place.

Activity Two

Addition pyramids are an easy way of structuring addition calculations. Answers can be easily checked with a classmate or the calculator.

Encourage students to explain the different mental strategies they used to add the numbers. For example, to calculate 47 + 58, students could use any of these strategies:

• Front-ending, that is, 47 + 50 → 97 + 8 → 105

• Adding the tens and then the ones:

40 + 50 → 90 + (7 + 8 = 15) → 105

40 + 50 → 90 + 7 → 97 + 8 → 105

• Adding the ones first and renaming as per the standard written algorithm:

Using this method, students add the ones first, rename the 10 ones as one 10, and then add the tens. Students could design their own pyramids and make them more interesting and challenging by leaving out different numbers in the pyramid.

Students could be encouraged to compare the speed of completing a pyramid using mental calculations with using a calculator.

**Activity Three**

This activity encourages students to use strategies for adding mentally and to practise their estimation skills. Students could share with a classmate their strategies for finding the sums.

#### Answers to Activity

**Activity One**

376 + 295 + 437 + 58 = 1166

**Activity Two
**2.

**Activity Three**

a. 285 + 396 = 681

b. 138 + 589 = 727

c. 377 + 396 = 773

d. 246 + 174 = 420

e. 467 + 174 = 641