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Riddle (simple arithmetic problem/illusion)
three girls have a friend 60 rupees and asked her to buy them a kilo of mangoes each from the market. the mangoes cost 55 rupees. to make it easy to divide the balance of 5 rupees, the friend kept 2 rupees and returned 1 rupee each to the the three girls.thus,the girls spend 19 rupees each and a total of 57 rupees.the friend kept 2 rupees,which makes the total 59 rupees. what happend to remaining 1 rupee?
The error lies in adding what the friend kept to what the girls spent. If you subtract instead, you get the $55$ rupees that the mango merchant got. To add up the $60$ rupees, you need to add $57$ rupees that the girls actually paid and $3$ rupees that they initially paid but got back from the friend; or $55$ rupees that the merchant now has, $2$ rupees that the friend now has and $3$ rupees that the girls now have.