Question 1181832
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A useful trick for performing mental multiplication is to multiply one of the numbers by some constant and divide the other by the same constant.<br>
For example, to multiply 24 times 35, you could cut the 24 in half to 12 and double the 35 to 70; then 12 times 70 is easier than 24 times 35 because one of the numbers now ends in 0.<br>
You can use the same kind of process to find as many combinations as you want of three dimensions that give the required volume of 200.<br>
Start with any single set of three dimensions, like your first one: 5*4*10.<br>
You can double the 5 and cut the 4 in half to get 10*2*10; that is your second one.<br>
Next you can double one of the 10s and cut the other in half to get 20*2*5, which is your third.<br>
Continue doing the same kind of thing.  If you want a set of dimensions that is not whole numbers, divide one of the measurements by a number that doesn't give a whole number result.<br>
Your third set was 20*2*5.  You can divide the 5 by 2 and double the 2 to get 20*4*2.5.<br>
Then you could take that and again divide the 2.5 by 2 and double the 20 to get 40*4*1.25.<br>
And you can continue with that process to get as many sets as you want that all give a volume of 200.<br>