Ali the animal keeper is checking and counting all the animals for her annual animal database. Help her to make sure her calculations are accurate.
More resources for Autumn Block 2 Step 18.
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Discussion points for teachers
1. How many birds must be in the bird boxes? Check your answer using an addition.
Discuss which calculation must be solved first. How can we then use an addition to check we have the correct answer? How will we know we have the correct answer?
132 – 59 = 73 in the bird boxes. 73 + 59 = 132
2. Explain Ali’s mistake.
Discuss which numbers are the parts and which is the whole. Which number must come first and why?
Ali has put one of the parts first rather than the whole. Her calculation should be 227 – 148.
3. Work out the missing numbers.
Discuss whether the parts or whole is missing in each example. What calculation would be needed to find the missing whole/ part? Why?
158 + 179 = 337; 243 – 155 = 88
4. Check the answers using the inverse calculation.
Discuss the inverse for each calculation. What answer should we reach if we are correct?
337 – 158 = 179; 88 + 155 = 243
5. Which calculation does Ali need to use and why?
Discuss what the greatest and smallest value could be, discuss how many different possible answers there could be.
206 – 117 because she is subtracting one of the parts from the whole to find the remaining part.
6. What could Ali’s two calculations have been?
Discuss how the numbers could be ordered for each calculation. What could the whole number of bats have been? How many of each type could there have been? How could we represent this using calculations? This question is open-ended for the children to explore.
Various answers, for example: 234 – 86 = 148; 234 – 148 = 86; 148 + 86 = 234; 86 + 148 = 234
National Curriculum Objectives
Mathematics Year 3: (3C3) Estimate the answer to a calculation and use inverse operations to check answers
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