Jack and Jones are brothers and they both sell apples for living. Jack sells 2 apples for 1 Rs and Jones sells 3 apples for 1 Rs. They each have 30 apples. Hence, Jack earns 15 Rs a day while Jones earns 10 Rs a day. This gives a total of 25 Rs.
One day Jack got sick and couldn't sell his apples. He gave his apples to Jones. Jones sold all 60 apples at price of 5 apples for 2 Rs (as 3 apples for 1 Rs + 2 apples for 1 Rs). At the end of the day, he counted the money and ended with a total of 24 Rs.
Where has Jones lost 1 Rs?
Answer
TL,DR: It is all about operator precedence
We have the following unit price for Jack apples: $1/2$.
We have the following unit price for Jones apples: $1/3$.
Thus making the calculation of the total amount collected: $$1/2 \times 30 + 1/3 \times 30 = 15 + 10 = 25$$ In that configuration, the unit price for a single apple is: $$(1/2 + 1/3) / 2 = 5/12$$
With the combined sale, we have the following unit price: $2/5$
Thus making the calculation of the total amount collected: $$2/5 \times 60 = 24$$
So far so good.
When we are comparing unit price of a single apple now.
The problem occurs because of operator precedence, $(1/2 + 1/3)/2 = 5/12 \ne 2/5$.
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