Question

The total cost c(x) of hiring a dump truck and an operator is described by the function c(x)=300+31x-3.90x^2 , where x is the number of hours worked. Find the number of working hours if c(x)=$220. in progress 0 5 months 2021-08-31T10:40:15+00:00 1 Answers 5 views 0 ## Answers ( ) 1. Answer: 2.05hrs Step-by-step explanation: Given he total cost c(x) of hiring a dump truck and an operator is described by the function c(x)=300+31x-3.90x^2 , where x is the number of hours worked. If c(x)=$220, then;

220  = 300+31x-3.90x^2

300+31x-3.90x^2 – 220 = 0

3.90x^2 + 31x – 80 = 0

x = -31±√31²-4(-80)(3.9)/2(3.9)

x = -31±√961+1.248/7.8

x = -31±47/7.8

x = -31+47/7.8

x = 16/7.8

x = 2.05

hence the number of working hours is 2.05hrs