Question

A solar-panel company counted 69 invoices at the end of the month. They charge $400 for a new installation and $25 fora service call. The total dollar amount of the invoices was $6,975. How many service calls were made?

Answer 1

Answer:

The number of service calls made = 55

Step-by-step explanation:

Let the total number of installations made by the company = x

Let the total number of service calls = y

Total number of invoices for the month = 69

=> $\[x+y=69\]$  -------------------(1)

Total amount of the invoices = $6975

=> $\[400x+25y=6975\]$  -----------(2)

From (1), $\[y=69-x\]$

Substituting in (2):

=> $\[400x+25*(69-x)=6975\]$

=> $\[400x+1725-25x=6975\]$

=> $\[375x=5250\]$

=> $\[x=14\]$

$\[y=69-x\]$

=> $\[y=55\]$