# Need urgent help with Related Rates

• Jul 22nd 2009, 08:41 AM
wdma
Need urgent help with Related Rates
Could anyone help me by solving this step by step so I can see what you did there?
Thank you so much in advance. (Wink)

http://10proxy.info/rr.png
• Jul 22nd 2009, 10:03 AM
Calculus26
R = 110q - q^2/200

dq/dt = 55 the rate production is increasing and q = 400

Now we differentiate with respect to time -- note d(q^2)/dt = 2q dq/dt

dR/dt = 110dq/dt -q/100 dq/dt

dR/dt = 110(55)-(400/100)(55)

dR/dt = 6050 - 220 = 5830dollars/day
• Jul 22nd 2009, 10:19 AM
wdma
Quote:

Originally Posted by Calculus26
R = 110q - q^2/200

dq/dt = 55 the rate production is increasing and q = 400

Now we differentiate with respect to time -- note d(q^2)/dt = 2q dq/dt

dR/dt = 110dq/dt -q/100 dq/dt

dR/dt = 110(55)-(400/100)(55)

dR/dt = 6050 - 220 = 5830dollars/day

Thank you so much Calculus26. I'm just uncertain about the last answer, a friend of mine told it can't be \$5830. He said that I might wanna try plugging in the derivative, but I 'm not sure what I'm getting wrong here.
Any ideas?
• Jul 22nd 2009, 10:35 AM
Calculus26
I am going to stand by answer--what does your friend suggest the answer

should be? What do you mean exactly by plugging in the derivative?
• Jul 22nd 2009, 11:45 AM
wdma
Quote:

Originally Posted by Calculus26
I am going to stand by answer--what does your friend suggest the answer

should be? What do you mean exactly by plugging in the derivative?

Your answer was definitely correct. My buddy was mistaken. Thank you again, Calculus26! (Clapping)