here's the tricky question:An open rectangular tub of uniform thickness 10cm
has external dimensions 165cm*100cm*75cm. What volume is required to completely
fill the tank?

Let's get the internal dimensions from the external dimensions and the
thickness of the walls and bottom:

1. To get the internal length, we must subtract the thickness TWICE from the
external length of the tub, once for the thickness on the left side and once
for the thickness on the right side. So the internal length of the tub is
165cm - 2×10cm = 165cm - 20cm = 145cm.

2. To get the internal width, we must subtract the thickness TWICE from the
external length of the tub, once for the thickness on the front side and once
for the thickness on the back side. So the internal width of the tub is
100cm - 2×10cm = 100cm - 20cm = 80cm.

3. To get the internal height, we must subtract the thickness ONLY ONCE from
the external height of the tub for the thickness on the bottom side. We are
told there is no top on the tub.  So the internal length of the tub is
75cm - 10cm = 65cm.

So volume of interior of tub = length×width×height = 145cm×80cm×65cm =
754000 cm³.

Edwin