Dewch i Feddwl Mathemateg (9 i 11 oed) Gwers 2 Bwydo’r Pysgod

# Lesson Plan

Abstract |

Does anyone have a pet fish? What is the special rule about feeding fish? – Not to overfeed them or they die. My next door neighbour went on holiday a few weeks ago and he told me to look after his fish. What sort of things will I need to think about if I’m looking after some fish? He was rushing off when he left, but he told me to be really careful not to feed them too much. |

Episode 1 |

IntroShow the children a picture of Resource Sheet A showing two fish. I think that my neighbour told me the baby fish eats 6 grammes of fish food every day. Does that sound about right? (Have some 5g weights available to show and confirm that this seems about right for a small fish.) So how much do you think the second fish would eat? The children will realise that the second fish is twice as big as the small fish (or that the smallest fish is half as big as the largest fish) and should therefore be fed: • 5 + 5 = 10g OR • 2 x 5 = 10g This can be shown using a multilink tower in two colours. Ask them how they can be sure the fish is twice as big. Children may suggest using rulers to measure, cutting out the smaller fish and laying it over the larger one, or folding the larger fish in half and laying it over the small fish. What if the little fish ate 7g a day? Or 4g? But actually, there were four fish in the tank. Show the children Resource Sheet B, showing a family of four fish. Can you work out how much each fish should be fed? |

Group DiscussionWork in groups using Resource Sheet B to calculate how much each fish should be fed. Decide on a sensible amount for the smallest fish and calculate proportional amounts for the larger fish, using coloured multilink to model if required. As an extension, for groups who finish quickly, ask them what if there was a fifth, larger fish in the tank – how much would it eat? |

SharingShare solutions and proofs, modelling using multilink towers. Ask the children about the relationship between the different fish ie the third fish is four times as big as the smallest fish, and the second fish is a quarter of the size of the second fish. Discuss the intervals shown by the multilink and note that they increase in size as the fish double. (NB It may be easier to graph the numbers using an A1 sheet of large squared paper.) Discuss what was the easiest way to check the relative sizes. Did everyone measure using rulers, folding or cutting? Or did some groups use the proportions of the fish alone? |

Episode 2 |

IntroDo you know, I was so good at looking after my neighbour’s fish that he told everyone all about how careful I was? And the week after that another neighbour went away and asked if I could look after their fish. Show the children Resource Sheet C with a different family of fish. This time, I definitely remember that the smallest fish had to have 4g of food. |

Group DiscussionWork in groups using Resource Sheet C and multilink to calculate how much each fish should be fed. As an extension, for groups who finish quickly, ask them what if there was a fourth, larger fish in the tank – how much would it eat? |

SharingShare results and proofs. Ask the children about the relationship between the different fish, noting that it can be described as one and a half times bigger or two thirds of the size. Discuss the intervals shown by the multilink and note how they increase in size. (NB Again, graphing using large squared paper may be useful.) How is this fish family different from the other fish family? Encourage the children to distinguish between the idea of doubling and one and a half times bigger, half and two thirds of the size. Discuss which is the easier to calculate – the first or second family of fish. |

Alternative episode for younger students |

IntroShow the children Resource Sheet D with a different family of fish – this time each fish increases to double in length, and width. Ask the children how much they think the smallest fish should be fed, and therefore how much each of the larger fish will need to be fed – compare to Resource Sheet A, where each fish doubles in length, but not in width. |

Group DiscussionWork in groups using Resource Sheet D. As an extension, for groups who finish quickly, ask them what if there was a fourth, larger fish in the tank – how much would it eat? |

SharingShare results and proofs. (NB Again, graphing using large squared paper may be useful.) Ask the children about the relationship between the different fish. Do the children think each fish should get double or four times the amount of its next fish? |

Reflection |