Task 49: Checking understanding of mental strategies for multiplication and division
Do these calculations by mental strategies, using the given starting point:
(a) 23 × 19 (use 19 = 20 – 1)
(b) 41 × 23 (use 23 = 1 + 2 + 4 + 16 and doubling)
(c) 408 ÷ 24 (use 10 × 24 = 240, 5 × 24 = 120, …)
(d) 408 ÷ 24 (divide both numbers by 2 to get an equivalent ratio)
(e) 319 ÷ 11 (write 319 as 99 + …)
Task 53: Using and applying mental strategies for multiplication and division
Try to answer this question within 30 seconds of reading it! Do not write anything down.
A shop offers a TV for £480 or 24 monthly payments of £25.25. How much extra do you pay if you go for the monthly instalments?
Task 55: Learning and teaching of mental strategies for multiplication and division
(a) A class calculates that to tile a bathroom wall with 13 rows of 37 square tiles you would need 481 tiles in total. Suggest how this might be done using relationships suggested by the rectangular array of tiles.
(b) The teacher then asks how we use the previous answer to work out many tiles would be needed for 13 rows of 38 tiles? A child replies 482. Identify the error here and suggest how to use this situation to promote learning.
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