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# Column subtraction 4: Lesson 3: walruses

## Learning Objective

We are learning how to subtract a 3-digit or 4-digit number from a 4 digit number using column subtraction (with more than one exchange, including exchanges across more than one place value).

Context: Whopping Walruses

https://www.bbc.co.uk/programmes/p03hn08v/player

Credit: BBC Two - Earth's Greatest Spectacles

## Clip Description

Walruses are found in the Arctic – a vast wilderness of snow, ice and sea. They are big and blubbery and have tusks that can reach 90 centimetres in length. They use their tusks to haul their massive bodies out of the sea and for smashing through sea ice to create breathing holes. They are very sociable creatures, preferring to rest together on land at ‘haul out’ sites that may contain thousands of individuals.

In this fascinating clip, walruses roll into the sea after a week-long siesta. Once in the water, they use their 500 sensitive whiskers to search for their favourite food on the seafloor: clams. We learn that a walrus may consume over 1,000 clams a day without eating a single shell.

## Whiteboard Number Challenge

We have learnt that the tusks of a walrus can reach 90 centimetres in length.

Can you use your knowledge of the 9 times table to write down your 90 times table?