[upwardbound]

Speaking of which, I want to warn everyone that I've found that Wolfram Alpha is not always mathematically precise! Here is an easy and concerning way you can repro this:

I noticed that if you put this formula into WolframAlpha, it gives a wrong answer. Input: 1’ 1” x 7’ 2.5” Primary result: 1125 sq inch (correct) Secondary result: 7.809 sq ft (WRONG) The correct sq ft is 7.8125 (exact) or 7.813 (rounded) Bug link: https://www.wolframalpha.com/input?i2d=true&i=1%E2%80%99+1%E...

[eesmith]

It looks like a rounding difference in the display. The exact answer is 1124.5, which when rounded up to 4 significant digits is 1125 sq inch. 7.809 sq ft is the correct answer in sq ft, again, rounded to 4 significant digits.

  >>> (1*12 + 1 ) * (7*12 + 2.5)
  1124.5
  >>> ((1*12 + 1 ) * (7*12 + 2.5) ) / (12 * 12)
  7.809027777777778

This is the decimal display of the closest float64 value to the exact rational answer of 2249/288 sq. ft (7 and 233/288 sq. ft., or 7 sq. ft. and 116.5 sq. inches).