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# Column subtraction 4: Lesson 1: bison

## Learning Objective

We are learning how to subtract a 3 digit number from a 4 digit number using column subtraction (with one or more exchanges, but not including an exchange across more than one place value).

Context: Bone-shaking Bison

https://www.bbc.co.uk/programmes/p04b58bm/player

Credit: BBC Two -Wild West: America's Great Frontier

## Clip Description

American bison are massive, shaggy beasts and the heaviest land mammals in North America. Females are called cows and males are called bulls. They live together for most of the year in small bands. However, they come together in very large herds in the summer breeding season. Sadly, this incredible species nearly became extinct in the late 19th century, when their population dropped from around 30 million to as little as 1,000 individuals.

In this fascinating clip, a herd of American bison can be seen in Yellowstone National Park. It is the breeding season and two large males are squaring up to each other, competing for a mate. We see them use their huge heads as battering rams in an awesome show of strength.

## Whiteboard Number Challenge

A baby bison is called a calf. Calves are born big. American bison calves can weigh a massive 32 kilograms at birth! (By comparison, the average human baby weighs 3.5 kilograms.)

Can you write down all the factors of the number 32?