Year 5 Maths Problem

[Royaldada]

Your help is needed please.

How can I explain this question to my Year 5 DD

Explain how you can use 8 x 7 = 56 to help you find 80 x 0.7 = 56

Any ideas would be welcomed

At Y5 level I'd guess it is about seeing that the tens have been moved around. What has happened here is that one number has been increased 10 times and the other decreased 10 times, but multiplying them together gets the same result. You are effectively moving the tens from one side of the sum to the other. (Another way of looking at it is that one number has been multiplied and the other divided, both by 10.)

Does she understand it without the decimal? Using easier numbers can sometimes help to make it clear. e.g 5 x 500 is the same as 50 x 50 - if they are secure in place value, they should instantly see that the zeros have moved but the total number of tens has remained the same and thus the product remains the same.

Equally does she understand the same sort of principle with addition and subtraction? So if you want to add 198 to 347 this is the same as adding 200 to 345 - you are moving some of the numbers from one side of the sum to the other.

Just playing around with changing the numbers in sums in different ways and seeing what happens to the result helped my son to cement these concepts.