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Column subtraction: Lesson 3: jellyfish

1 - Learning Objective

Learning Objective

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

Context: Jellyfish


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Credit: BBC Two - Atlantic: The Wildest Ocean on Earth

Clip Description

Jellyfish are found in all of the world’s oceans. They come in many shapes, sizes and colours. The smallest jellyfish are only the size of a thumbnail. The largest ones, like the lion’s mane jellyfish, can grow to a size of 2 metres 30 centimetres across. Jellyfish aren’t fish! In fact, they couldn’t be more different as they don’t have bones, eyes, ears, a heart or a brain!

In this fascinating clip, hundreds of slow-moving cassiopea jellyfish are on their way to a sunbathing party. When they find a sunny spot, they sink to the bottom of the ocean and use the sunlight to grow algae on their bodies. The jellyfish rarely need to hunt because they feed off the algae.

Quick Number Challenge

We have learnt that the lion’s mane jellyfish can be as much as 2 metres 30 centimetres across. 2 m 30 cm is the same as 230 cm.

How many different ways can you make 230?

e.g.  100 + 100 + 20 + 10 = 230           250 – 20 = 230