Being efficient means finding a way to solve a problem quickly whilst also maintaining accuracy.

A mental strategy is a method chosen to find something out which can be done in your head or with some jottings.

The process of unitising and exchanging between place values is known as regrouping.

Decide on the most efficient subtraction strategy, including column subtraction 

Maths

In this unit pupils will revisit column addition with regrouping and column subtraction with exchanging to solve problems. They will read Roman numerals to 100. In the future unit pupils will consolidate column addition with regrouping and column subtraction with exchanging to solve problems. They will use known facts and strategies to accurately and efficiently calculate and check.

In the prior unit pupils identified the minuend and the subtrahend in column subtraction and explained the column subtraction algorithm. They subtracted from a 2-digit number using column subtraction with exchanging. In this unit pupils will revisit column addition with regrouping and column subtraction with exchanging to solve problems. They will read Roman numerals to 100.

Review of column addition and subtraction

Which calculations would it be most efficient to answer using a mental strategy? 

Which calculations would it be most efficient to answer using column subtraction? 

What is the most efficient way to calculate 368 − 99 =? 

What is the difference between 292 and 288? 

Evie and baby Elias have a total length of 605 cm. If baby Elias has a length of 205 cm, how long is Evie? Evie is {{ }} cm long.

Elodie and baby Emily have a total length of 611 cm. If Elodie has a length of 437 cm, how long is baby Emily? Emily is {{ }} cm long.

Regrouping is needed in the ones and tens. 

Where is regrouping needed in this column subtraction?

Complete the column subtraction. What is the difference between the two numbers?

Calculate the difference using column subtraction.

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