How do you find the cost of a gallon of water if the cost of a gallon of milk is $0.50 more than five times the cost of a gallon of water and if a gallon of milk costs $3.75?

1 Answer
Mar 4, 2018

Answer:

A gallon of water costs #$0.65#

Explanation:

Problems like this can be confusing because it's hard to figure out how to express amounts like "$0.50 more than five times the cost of a gallon of water."

The trick is to write the math expression one step at a time.

Find a way to express the cost of a gallon of milk

Let #x# represent the cost of a gallon of water

Cost of water . . . . . . . . . #x# #larr# cost of a gallon of water
#5# times as much . . . . . .#5x#
#50ȼ# more than that . . . #5x + 50# #larr# cost of a gallon of milk

Write the equation and solve for #x#

#5x + $0.50 = $3.75#
Solve for #x#, already defined as "the cost of a gallon of water"

1) Subtract #$0.50# from both sides to isolate the #5x# term
#5x = $3.25#

2) Divide both sides by #5# to isolate #x#, already defined as "the cost of a gallon of water"
#x = $0.65# #larr# answer for "the cost of a gallon of water"

Answer
A gallon of water costs #$0.65#

#color(white)(......)# ――――――――

Check

#1# gallon of water . . . . . #$0.65#
#5# times that . . . . . . . . . .#$3.25#
50ȼ more than that . .. .#$3.75#   ✓

#Check#