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Column subtraction 4: Lesson 2: brittle stars

3 - Whiteboard Challenges

Spot the Mistake!

Someone has made a mistake in their column subtraction. Can you explain the mistake to your talk partner?

Did you know?

In a similar way to a lizard, who can shed its tail to fool and escape a predator, a brittle star can detach one or more arms from its body if caught. Incredibly, the arms are able to grow back (though this may take several months or even years).


Use PAWS, counters and column subtraction to solve the following word problem.

1,565 kilometres off the coast of Antarctica, a cluster of 2,503 brittle stars had linked arms, hoping that they would not get swept away by the strong ocean currents. Of these brittle stars, 1,366 had one or more arms missing. The remaining brittle stars had a complete set of arms.

How many brittle stars on this patch of ocean floor had no arms missing?