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A story about doubling

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Transcript

  • 1. A STORY ABOUT DOUBLING
  • 2. Mrs Hippo has lost all the little hippos from her class. She is very forgetful teacher. She doesn’t remember how many little hippos belong in her class. Before we start looking, can we help Mrs Hippo work out how many little hippos are in her class?
  • 3. Mrs Hippo thinks and thinks and then she remembers! There were 8 groups of little hippos. There were 3 little hippos in each group. Um…. How many is that altogether? We could add all the groups together, but because we know that each group of little hippos is the same we can work it out another way.
  • 4. Let’s look at the first group of little hippos. How many hippos can you see? We can see three little hippos standing together.
  • 5. Look! More little hippos have joined the first group. How many little hippos are in this group? There are three more little hippos. Put your thinking caps on to work out how many little hippos altogether. How could we easily work it out? We have two groups of three hippos in each group. We can double the number in each group, so double 3 is 6. This means 3 by 2 is 6. We have found six hippos.
  • 6. More little hippos have joined their friends. How many more little hippos can you see? There are two more groups of three, so there are six more little hippos. Put your thinking caps on to work out how many little hippos altogether. Now we have four groups, with three hippos in each group. We can double and then double again. If double 3 is 6, 3 multiplied by 4 means double 6, which equals 12. So 3 by 4 is 12. We have found 12 hippos now.
  • 7. We can see lots more little hippos. How could we easily work it out how many now? Remember we don’t need to count each one! Count the number of groups. Now we have eight groups, with three hippos in each group.
  • 8. To work out how many little hippos altogether we can use the doubling strategy. We can double, double and then double again. We start with our first group of three little hippos.
  • 9. We double the group of three. Double 3 is 6.
  • 10. We double again. Double 6 is 12.
  • 11. Finally we double, double, double. So double 12 is 24. Altogether we can see 24 little hippos. 8 groups of 3 makes 24. Mrs Hippo needs to find 24 little hippos. This story about doubling showed us a special strategy where we can double, double, double when there are eight groups of equal numbers.