Posted by **joelle** on Thursday, April 8, 2010 at 12:45pm.

The average cost per item, C, in dollars, of manufacturing a quantity q of cell phones is given by

C= (a/q) + b

where a and b are positive constants

a.Find the rate of change of C as q increases. What are its units?

b. Currently, 5000 phones are being made and production is increasing at a rate of 100 cell phones per week. How fast is the average cost changing if a = 200000? Is the average cost increasing or decreasing

for a i got C(q)= (a/q) + b

C'(q)= -(a/q^2) DOLLARS PER CELL PHONE.

for b) i started off as

dC/dt =-a/q^2 dq/dt =

(-200000/q^2).100

IM LOST AND NOT SURE WHAT TO DO PLEASE HELP ME

- math Please help me with part b -
**joelle**, Thursday, April 8, 2010 at 12:48pm
also can you please tell me if A is right? thank u

- math Please help me with part b -
**bobpursley**, Thursday, April 8, 2010 at 1:35pm
a, No.

YOu want dC/dq (which is cost/unit)

dC/dq=-a/q^2

b) dC/dt=-a/q^2 dq/dt

dC/dt=-2E5/25E6 *1E2=-20 dollars /week

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