A grocery store has 4 kinds of jelly. They sell grape jelly twice as much as strawberry jelly, and raspberry jelly twice as much as plum jelly. The raspberry jelly sells a third as much as the grape jelly. If they sold 6 jars of plum jelly today, how many jars of strawberry jelly did they sell? Let's be accurate as possible.
They sell twice as much raspberry jelly as plum jelly, so they sold 2 * 6 = 12 jars of raspberry jelly today. The raspberry jelly sells a third as much as the grape jelly, so they sold 12 * 3 = 36 jars of grape jelly today. The grape jelly sells twice as much as the strawberry jelly, so they sold 36 / 2 = 18 jars of strawberry jelly today.
The answer: 18.