If a farmer can trade seven plums for two apples, three apples for two pears, and six pears for a watermelon, what is the minimum number of whole plums he needs to trade for 5 watermelons?

Question

If a farmer can trade seven plums for two apples, three apples for two pears, and six pears for a watermelon, what is the minimum number of whole plums he needs to trade for  5 watermelons?

mathmate · Answer

It's a cascading ratio,
(6/1)*(3/2)*(7/2)
=31.5
=32 whole plums

mertsj · Answer

He needs 30 pears for 5 watermelons.  30 pears requires 45 apples.  45 apples requires 22.5 times 7 plums so he needs 158 plums

mathmate · Answer

Look at it this way:
Pl A Pe W
7 :2
    3 :2
         6 :1
It will make it much easier to understand

mathmate · Answer

Sorry, for 5 watermelons, multiply 31.5 by 5 to get 157.5 or 158 whole plums, same as Mertsj's answer.