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The Size of a Horse

Consider this formula: f(W) = (0.1)W2/3

Animal physiologists claim that this formula determines the surface area of a horse (m2) as a function of its weight (kgs).

Also, suppose you can't get a horse to balance on a bathroom scale. The "cowboy's rule-of-thumb" is to use this formula:

Weight {[(Heart girth)2 x length]/300} + 50

where the heart girth and length are measured in inches, producing a weight in pounds.

Task 1: How can you adjust the constant of 0.1 in the first formula so that computations can be made in English units and not metric units?

Task 2: How would you gather data to check on the validity of both of these formulas?

Note: In case you are curious (and you are), Tabler's Cyclopedic Medical Dictionary (1993) claims you can calculate the surface area of human skin by this formula:

S.A. = (0.007184)(your weight in kgs)0.425(your height in cms)0.725

Source: K. Kalmanson & P. Lenschaft's Mathematics: A Practical Approach, 1978, p. 41