Length: take out the left and right cubes that touch the inside, thus u have 58. Breadth: take out the left and right cubes that touch the inside, thus u have 10. Height: take out the bottom cube that touches the inside, thus u have 29. Hence 58x10x29.

Why must take out 1cm from side?

because the cubes at the sides are touching the inner side of the container

This Q has been posted before

K. Tks

Can someone show me what went wrong with my workings?

hmm..i'm also working the question out. Not sure how you managed to get 19 units to represent 819.. i got 19 units to represent 273..which gives me a decimal..something doesn't seem quite right here

I would like to point out the following: (1) Yeo See Yeong's 'unit' does not represent the same unknown/factor as Tan Weiqiang's 'unit' so although both working show 19 unit = ... differently, the calculation towards finding the answer will have the same answer (2) There is a mistake in the question. If we change the figure 273 to 266, we should be able to work out an answer (3) the solution offered by the school teacher doesn't seem to have any connection to the problem so there could be a mistake there (maybe it's for a different question) (4) The presentation of the working contain some conceptual errors -- we should never write 11/35 = 154 because they represent numbers and these two numbers are certainly not equal. It should be 11 units == 154, 1 unit = 14.

Thank you Vei Li Soo. I think there's a little typo in your point #1 Yes..Mr Yeo See Yeong's 19 units is different from my 19 units..so although the number is the same, the results will be different. #2- I agree that the question has an error...this should be typically a pretty straightforward question..so should not have decimals in the computation. #3- yup..just saw the solution posted up by the parent...cannot link it to the question because personally, I could not see where the numbers came from. #4- Units being equated to numbers is a very common error..unfortunately..Guess we have to consistently put up the 'correct' one so that people realise why. Cheers Vei Li Soo. Thanks for pointing these things out. :)

For point (1), I meant that the answer (or result), which is the number of cards they have altogether, will be the same. :)

Thanks all... I will double check with the teacher if there's any error in the question when school reopens.

Assume all are $2, then there will be: 120 x $2 = $240 This value differs with the actual amount by $129. This is because of the $3-value difference between each $2 and $5 note. Hence, Number of $5 notes = $129/$3 = 43. (Answer)

Thanks!