Expert: Sherry Wallin - 7/12/2011

Question
I've been trying to do this question all night, so I need some help. Here it goes:

The weight of a bass varies jointly with the girth and the square of the length. A 22 inch long bass with a girth of 15inches weights about 6 pounds. How would I set this problem up. I keep getting this off the wall number that doesn't make sense.

Answer
Hi Nessa~

Ok, well then you need to just use the formula for the varies jointly and that is if y varies jointly as x and z then y = kxz.
Now think about what the problem is saying about x and z. they say that x is the girth and z^2 is the length, so

Let w = weight and
g = girth and
L = length

so now you have w = kgL^2

You are given L = 22 in and g = 15 in and w = 6lb so
6 = k*15*22^2 => 6 = 7260k => k = 6/7260 ~= .000826446

thus w = .000826446Lg

Math Prof