May 2014

Kepler-186f Space discovery: Using NASA's Kepler Space Telescope, astronomers have discovered the first Earth-size planet orbiting a star in the "habitable zone" -- the range of distance from a star where liquid water might pool on the surface of an orbiting planet. The discovery of Kepler-186f confirms that planets the size of Earth exist in the habitable zone of stars other than our sun. Read more ....

Gecko Learning from animals: A research team has moved technology to manufacture high-quality dry adhesives that mimic the stickiness of gecko's feet to the threshold of commercial production. Read more ....

Traffic Hybrid vehicles: What makes cities in India and China so frustrating to drive in -- heavy traffic, aggressive driving style, few freeways -- makes them ideal for saving fuel with hybrid vehicles, according to new research by scientists at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab). Read more .....

Atlantic Ocean floor Life's origins: Life took root more than four billion years ago on our nascent Earth, a wetter and harsher place than now, bathed in sizzling ultraviolet rays. What started out as simple cells ultimately transformed into slime molds, frogs, elephants, humans and the rest of our planet's living kingdoms. How did it all begin? Read more ....

Enceladus Space discovery: NASA's Cassini spacecraft and Deep Space Network have uncovered evidence Saturn's moon Enceladus harbors a large underground ocean of liquid water, furthering scientific interest in the moon as a potential home to extraterrestrial microbes. Read more ....

Neurogrid Brain on microchip: Stanford scientists have developed a new circuit board modeled on the human brain, possibly opening up new frontiers in robotics and computing. Read more ....


Did the question confuse you? That was the sole purpose - to confuse you. Otherwise, there is hardly any substance in the question.

In the present case, there is a single Rs 500 counterfeit note in circulation. So the loss suffered by the receiver can neither be more nor less than Rs 500. The loss has to be Rs 500.

Let's look at the question differently - we change the chronology of events slightly which, however, does not change the complexion of the question.

First, the customer enters the shop and buys the pen. Let's assume that the shop-keeper has enough change to satisfy this transaction. Therefore, he hands over the pen and Rs 300 to the customer. The cheat goes away with the pen and the money. The shop-keeper is unaware that the 500-rupee note is fake. But, in fact, he has suffered a loss of Rs 500 (Rs 200 worth pen and Rs 300 in cash).

Now, in anticipation of more customers, the shop-keeper needs change. He, therefore, goes to the neighbouring shop-keeper and requests for change. He hands over the 500-rupee note to the neighbour who gives him five 100-rupee notes (or whatever change) in exchange. But even before the shop-keeper can walk out of the shop, the neighbour has doubts and examines the 500-rupee note, and finds it to be fake.

"Hey, this is fake," the neighbour tells. He returns the fake note to the shop-keeper and takes back his five 100-rupee notes. It was as though this exchange had not occurred at all! It was as if the shop-keeper had not met his neighbour at all - the fake 500-rupee note continues to remain in his possession, and the neighbour has the five 100-rupee notes as though he had never parted with them!

Some useful links for
your career:

  • Union Public Service Commission -
  • IIT-Kharagpur -
  • Indian Statistical Institute -
  • Indian Institute of Technology Madras -
  • Indian Institute of Management, Ahmedabad -
  • Indian Institute of Mass Commission -
  • IIT Bombay -
  • Indian School of Mines, Dhanbad -
  • Birla Institute of Technology, Ranchi -
  • Central Institute of Fisheries Nautical and Engineering Training -
  • Indian Institute of Information Technology, Allahabad (Deemed University) -
  • Central Marine Fisheries Research Institute, Kochi -
  • Tata Institute of Social Sciences, Mumbai -

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