Mammy is out of the kitchen and it's a great opportunity to get you hands on that

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Question:

Mammy is out of the kitchen and it's a great opportunity to get you hands on that cake inside the fridge. Alas, Daddy has the same idea and also rushes to the same end! Your Dad wishes to negotiate and offers you 3 out of the 20 pieces of the pie. You figure that offers back and forth will take 5 seconds each to respond. Meanwhile the cake melts at a rate of 1 /50 every second and Mammy will be back in the next 20 seconds. Should you accept Daddy's offer or not? Explain briefly