Jeff and his family are driving to visit his grandmother. They have driven about 30 miles, which is 2/3 of the way. How much further do they have to go?

Let us assume the total distance Jeff and his family has to go = x

Distance that have already been covered by Jeff and his family = 30 miles

Then

2x/3 = 30

2x = 30 * 3

2x = 90

x = 90/2

= 45 miles

So

The further distance Jeff and his family has to go = (45 - 30) miles

= 15 miles

So the distance that is still required to be covered by Jeff and his family to visit his grandmother is 15 miles.