Algebra

I really need extra credit in my Algebra class, so my teacher told me if I could answer this question, I would get bonus points. Either this question is for Einstein, or I'm missing some sort of equation.
"A particular disc can be made to rotate at 2 different speeds. If it were made to rotate slower by 135 revolutions per hour, it would require an additional 2.7-hours to make 315 revolutions. Find the higher speed at which it can operate."

That's all the question says...Could someone help me?

When do you need the answer by?

The 10th.

I'll work on it this Friday when my brain is emptied of school stress

Thanks man.

no mater how i do this i always get a decimal point, are you sure it didn't say anything else, or perhaps he would be willing to rephrase it?

I'll try to find an answer for you before Monday.

That's exactly what it says, Preid. Nothing more and nothing less. I don't think the answer would be a decimal, but it might be.

Is the speed reduced to 135 or the orginial speed is x and the new speed is x-135?

It's x-135

Does this help:

x = higher speed in rev/hr
Tf = time for the higher speed to complete 315 rev


315/x = Tf

315/ (x-135) = Tf +2.7

solve simultaneously



315 / (x-135) = (315 / x) +2.7

315x / (x-135) = 315 + 2.7 x

315 x = 315 x - 315 (135) + 2.7 (x^2) - 135 (2.7)x

2.7 (x^2) - 135 (2.7)x - 315 (135) =0

2.7 (x^2) - 364 x - 42525 = 0

use quadratic formula:

two answers are 209.86 rev/hr and -75 rev/hr

take the positive answer.

I had Algebra so what i did is make up numbers and place them all around the paper with a bunch of signs and go to the back of the book and take the right answer and put it ina box.. i always get it right and the teacher never caught me!

Good Job Gman

Thanks Gman.