Mental Calculation

Study content

• use factors of a number to aid mental computation involving multiplication and division

Learning goals

• Be able to implement different mental calculations methods

Working Mathematically

• compare initial estimates with answers obtained by mental methods and check by using

a calculator (Problem Solving)

Description of Lesson:

• Orientation [5 mins] - As a class, spend time going through the homework task. Does anyone notice commutative laws, associative laws and distributive laws help you calculate without calculation.
• Introduction [10 mins] - Mental calculation is the art of exclusively using human brain to perform arithmetical calculations without any help from other supplies like calculators. Plus, question: " Do you want to be genius? Mental calculation could make your friends think you are genius.

Discuss: 15+37+18+45+22=?

Which law you are going to apply for this calculation in your mind? (Commutative laws)

Introducing mental calculation with distributive law. For example, 47*2= (40+7)*2=80+14=94 ; (1/2)*192=(1/2)*(180+12)=90+6=96; 17*9=17*(10-1)=170-17=153. It also could call splitting (mental).

• Activity 1 [20 mins] – Bang Activity

Get everyone to stand in a circle facing inwards. The teacher running the game will need to stand in the middle of the circle. For example, the teacher says 23-5 and points at someone in the circle. That student must duck down straight away and the two people either side of them must say 18 as soon as possible and yell "bang". Whoever say out the answer at last is out. Then game continues. When there are only two students left, they stand back to back, and the teacher starts counting. With each count the two people take steps away from each other. The teacher then say a 23 × 9, and the two people turn and say out 207 and yell "bang". The person who is fastest wins.

• Activity 2 [10 mins] – Online Practice https://amsi.org.au/ESA_middle_years/Year7/Year7_md/Year7_1c.html#stucontest-5
• Conclusion [5 mins] – Teacher-led discussion recapping the key learning ideas and highlighting any patterns in mental calculation strategies.
• Homework- have students complete this Mental Calculation Worksheet in the mind and remember the process of the calculation. Next lesson, the teacher will ask how to get the answer.

Lesson Power Points

Reflection question: Were the students engaged and motivated in “Bang” activity?

How was "Bang" activity effective in mental calculation?