Hi Guys,

Can someone please confirm why did we multiply the 3 heights together instead of adding them?

The correct answer is 150 but the trap answer is 450.

Hi Guys,

Can someone please confirm why did we multiply the 3 heights together instead of adding them?

The correct answer is 150 but the trap answer is 450.

Not sure what you mean; the volume is just

\frac{20}{3} \times 5 \times (2 + 1.5 + 1)

That’s equal to 150.

I took the height as 2+1.5+1. In doing so I was forming a longer cuboid of h=4.5, w=5 and l=20.

I ended up choosing 450.

I think you’ve found your mistake.

Can we not stack the 3 figures on top of each other- so to say to form a cuboid?

You can - horizontally (i.e, you’ll still have three separate cuboids). What you can’t do is to combine them to a single, large, cuboid.

In general wouldn’t stacking them up vertically, a shortcut we usually look for?

Does any part of this question suggest we can’t do this here? I usually try to minimize the fractional calculation be regularizing the figures and it mostly leads to the correct answer.

The problem is that the question is clearly modelled on three separate, horizontal cuboids. Shortcuts are nice, but you must make sure that they are valid. Trying to “stack” them to one large cuboid would not make them valid, since that changes the question entirely. From the perspective of the question, you’re removing the divisions and assuming that the height of the **entire** pool is 2 m. Clearly that’s a different problem.