The demand function for a certain brand of mattress is given
     The demand function for a certain brand of mattress is given by  p = 600e^-0.04x  where p is the unit price in dollars and x (in units of a hundred) is the quantity demanded per month. (Round your answers to the nearest integer.)  (a) Find the number of mattresses demanded per month if the unit price is set at $400/mattress.  mattresses  (b) Use the results of part (a) to find the consumers\' surplus if the selling price is set at $400 per mattress.$  Estimate the present value of an annuity if payments are $1300 monthly for 15 years and the account earns interest at the rate of 10%/yr compounded continuously.   
  
  Solution
a) P = 600e^-0.04x
p = $ 400/mattress
400 = 600e^-0.04x
solve for x: ln(4/6) = -0.04x
x = 10.136 = 10 mattress
b) revenue = 400*10 = $ 4000
Deman = p*no. of matress = 400*10 = $4000
There is no surplus 0 $

