Six chimps  were introduced to a slot machine called the Chimp- O- Mat, which would give out one grape when a white coin was insert into the slot. When Dr Wolf showed a young chimp named Moos how he could win himself a grape by inserting a coin, Moos immediately picked up another coin, pushed it into the slot, then stuck out his paw and waited for a grape to drop out.. Besides white coins, the chimps were given yellow coins to insert into the slot, but nothing came out because they were worthless. The chimps soon learned this fact. When a handful of white and yellow coins were thrown into the cage housing, Bula, Bimba and Alpha, the three chimps rushed for the white coins and never touched the yellow ones. Now the chimps were madly in love with money. Would the six chimps value money enough to work for it? To find the answer, Dr Wolfe designed a work machine. The chimps were shown that when a large handle was lifted, they could pick one grape. When they had learned the skill of lifting the handle to get the grape, Dr Wolf made a change to the machines so that instead of the grape they would find a white coin. This coin would still buy them one grape at the Chimp- O- Mat. Thus the complexity of getting a grape was not only doubled, but also the money to buy the grape could be achieved only by honest work. The handle they had to lift to get the coin weighed eighty pounds. Great effort is needed for a young chimp to raise that weight, yet the formerly lazy chimps not only quickly mastered the new operation, but also showed great eagerness to work for money. In the first part of the experiment the chimps learned to   _  .
tell the difference between the useful and the worthless coins use yellow coins to get grapes wait for the grapes to drop out buy grapes with coins