# Rational Expressions

• Nov 11th 2010, 07:02 PM
Ravangerz
Rational Expressions
I have been trying a couple problems for the past hour and am having a hard time.
Could someone please walk me through each, or even one of the problems?
If you solve it could you please show work so I can learn?
Thank you so much!

1. A family travels 18 miles downriver and returns. It takes 8 hours to make the round trip. Their rate in still water is twice the rate of the current. How long will the return trip take?

2. The circumference of a circle varies directly as the diameter. A circular pizza pie with a diameter of 1 foot has a circumference of 3.14 feet. What will be the circumference of a pizza pie with a diameter of 1.5 feet?
• Nov 11th 2010, 07:13 PM
pickslides
Quote:

Originally Posted by Ravangerz
1. A family travels 18 miles downriver and returns. It takes 8 hours to make the round trip. Their rate in still water is twice the rate of the current. How long will the return trip take?

So 8 hours in total, as the rate is twice as much on the return (r) as the downriver part (d) then $2r=d$ and $8 = r+d \implies 8=r+2r \implies r = \frac{8}{3}$

Quote:

Originally Posted by Ravangerz

2. The circumference of a circle varies directly as the diameter. A circular pizza pie with a diameter of 1 foot has a circumference of 3.14 feet. What will be the circumference of a pizza pie with a diameter of 1.5 feet?

$C\propto d \implies C=kd$ and $d=1$ when $C=3.14$ solve for $k$ when $3.14 = k\times 1$
• Nov 11th 2010, 07:33 PM
Ravangerz
Ahh got it
thanks alot!