The associative law states that it doesn't matter how you group or pair values (i.e. which we calculate first), the result is still the same. It applies for addition and multiplication.

Working efficiently means finding a way to solve a problem quickly whilst also maintaining accuracy.

Explain when it is efficient to use factorising or long multiplication to multiply by 2-digits

Maths

In this unit pupils will learn to multiply a 3-digit by a 2-digit number They will use accurately short and long division and use a ratio chart to solve short and long division. In the future unit pupils will add, subtract, divide and multiply with integers, decimals, positive and negative values.

In the prior unit pupils will multiply a 3-digit number by a single-digit number using expanded and short multiplication. In this unit pupils will learn why the product stays the same when one factor is doubled and the other is halved and explain the effect on the product when scaling the factors by the same amount. 

Multiplying and dividing by 2-digit numbers

Select equivalent expressions to 21 × 30

Which method is more efficient to solve 47 × 16 = ?

Which method is more efficient to solve 132 × 15 = ?

Which factorised example would be most efficient to solve 36 × 12?

Use an efficient method to solve: The Olympic event is selling tickets. Each ticket costs £32 and 29 tickets are sold in the first five minutes. What is the total amount spent? £{{ }}


Use an efficient method to solve: 407 × 15 = {{ }}

Look at the numbers below and select the composite numbers.

Select the equivalent expressions which would make this equation correct.     36 × 24 = 

Find the expressions that are equivalent to 35 × 4 × 8 

Look at the equation. Find the missing number.     42 × 49 = 42 × 7 × {{ }}

This lesson will soon be taken down.

Explain when it is efficient to use factorising or long multiplication to multiply by 2-digits

Lesson outcome