Question 456897
At the car wash there is a flat fee for the first 8 minutes.
 Sally was there for 12 mins and cost her $5.
 John was there for 17 mins and cost him $6.25.
 Write a equation and find the cost of the flat fee and cost per minute.
:
Let f = flat fee for the 1st 8 min
Let a = cost for each additional min
:
Two equations:
:
"Sally was there for 12 mins and cost her $5."
a(12-8) + f = $5
4a + f = $5
:
" John was there for 17 mins and cost him $6.25."
a(17-8) + f = $6.25
9a + f = 6.25
:
We can use elimination here, subtract the 1st equation from the 2nd
9a + f = 6.25
4a + f = 5.00
-----------------subtraction eliminates f find a
5a = 1.25
a = {{{1.25/5}}}
a = .25 for each additional min
:
Find f using the 1st equation
4(.25) + f = 5
1.00 + f = 5
f = 5 - 1
f = $4 is the flat fee for the 1st 8 min
:
Check our solutions in the 2nd equation
9(.25) + 4.00 = 6.25