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 ....

Fake note

Bank note

Recently while reading the news I came across the following headline "What to do if ATMs spew out fake notes for you". I was alarmed. Do even ATMs deliver fake notes?

While on the subject of fake notes, I remember a very simple teaser that a friend of mine had asked me few years ago. It was a simple question, involving simple arithmetic. I had answered almost promptly (of course, it is an altogether different matter that my answer was wrong. The fact remains I had answered almost immediately).

This is what my friend had asked me: A customer goes to a shop and buys an expensive pen worth Rs 200. The customer hands over a Rs 500 note to the shop-keeper. However, the shop-keeper does not have change and, so, goes to the neighbouring shop and gets change.

He comes back, hands over the pen to the customer and also Rs 300 in change that is due to the customer. The customer walks away with the pen and the money. There were a few more customers after that, and the shop-keeper now had enough change. But it proved to be lean day thereafter and there were no more customers to cater. The shop-keeper dozed off.

After some time he found himself rudely shaken, and woke up. He found standing before him the neighbouring shop-keeper.

"Hey, the Rs 500 you gave me is fake," the neighbour told him.

The poor shop-keeper had to take back the counterfeit note, and hand over five crisp 100-rupee notes to the neighbour. The question is: How much loss has the shop-keeper suffered. Can you help me answer this question?

Click here for the solution


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  • Union Public Service Commission -
  • IIT-Kharagpur -
  • Indian Statistical Institute -
  • Indian Institute of Technology Madras -
  • Indian Institute of Management, Ahmedabad -
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  • 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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