Expert: Scott A Wilson - 2/26/2011

Question
Hi
I'm alittle confused with this question and the y-intercept.

Selina is filling the bath tub at a rate of 3inches every 4minutes

a)write an equation for the total number of inches of water for x minutes of filling.

I think it's y=3/4x+b

b) Explain the y-intercept
c) The tub filles for 8min, how deepis the water?

I'm not sure if part a is correct, therefor I'm lost for part b and c

Am i on the right track?

Answer
Yes, you've got it done correctly so far.  Just so we both know the x is in the numerator,
I find it easier to write y = 3x/4 + b.  In higher math, some people write y = 3/4x
and really mean 3/(4x).  Putting it as 3x/4 avoids this confusion.

The y-intercept is where the line crosses the y axis.
Given that a problem is in the form y = mx + b, m is the slope and b is the y-intercept.
Here, we have the slope as 3/4 and the y intercept as b.

Since the tub starts empty at time 0, that means that b = 0.
Thus, the equation is y = 3x/4.

For (c), it says the tub had been filling for 8 minutes, so put in x = 8".
This means that y = 3*8"/4 = 24"/4 = 6".