It seems that the dimensions first have been converted to millimeters using the approximate factor 25mm/in (instead of the exact 25,4mm/in) and that the obtained volume in cubic mm has been converted back to cubic inch by dividing by the factor int(25,4**3)=16387.

25*18*11*int(25,4)**3/int(25,4**3)=4950*0,953499725392079=4719,82364069079, which rounds to 4720 cubic inch with a relative error of about 40/10**6. ]]>

I would use this problem or a similar problem in class. I would probably bring in a couple of suitcases to help students work through it. I must admit that, when I first began thinking about this problem, I forgot about the reduced capacity due to the materials.

]]>It’s possible that it’s not an actual error, but that the capacity is less than the product of the dimensions because of thickness. There might be some padding on the front or back that shaves off a bit.

(pausing while I play around with Wolfram Alpha)

Actually, if you keep the longest dimensions the same, but drop the shortest by half an inch, 25x18x10.5 is 4725, which is really close. This would represent a quarter inch of padding on front and back (top and bottom? The two biggest sides.) So it might just be something like that.

I wish I knew what, though — it looks like all their luggage has that same lower-capacity-than-expected even just in inches.

]]>I think there is a second error. It is a basic calculation error before the conversion is even done. 25 x 18 x 11 equals 4950 so the capacity would be 4950 cubic inches, right? Or might there be some rounding happening somewhere?

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