Lynn put 7/8 gallons of gas in her tank. If there are now 18/6 gallons in the tank, how many gallons did she start with

17/8 gallons

Step-by-step explanation:

18/6 gallons in the tank.

Before that, she fill 7/8 gallons.

So,

18/6 - 7/8

Subtracting both of these are impossible since the denominators are not equal.

We can do this by multiplying each other's numerator and denominator by their other denominator.

6 * 8 = 48

18 * 8 = 144

8 * 6 = 48

7 * 6 = 42

144 / 48 - 42 / 48

We can now subtract this. Note: do not subtract the denominator.

144 - 42 = 102

102 / 48

17/8

So,

There is 17/8 of gallons in the tank before filling it.