Classic interview brainteasers

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1. When the time is 3:15, what is the angle between the hour and minute hand?
2. There are 10 machines producing gold coins. One of the machine is producing coins that are one gram light. If you can only weigh once, how can you tell which machine is making defective coins?

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Aviator

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1. 0 degrees
2. Ask the machine

Nepal ko chora

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Answer for the first question should be "7.5 degrees" since hour hand moves slightly away from 3 o'clock position in 15 minutes.

Poon-Hill

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7.5 degrees??? How did u get that answer?

Nepal ko chora

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Poon-Hill,

Hour hand moves at the rate of 30 (= 360/12) degrees per hour. So, hour hand moves 30/4 = 7.5 degrees away in 15 minutes from 3 o'clock position. Hence, the angle between hour and minute hand at 3:15 will be 7.5 degrees. Hope that helps.

Aviator

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krishnaram

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The answer to the second question:

Take one coin from the 1st machine, 2 coins from the second machine, 3 coins from the third machine and so on. Measure the weight of the coins. If the obtained weight is one gram short of the expected result, 1st machine is producing defective coins, and if the obtained weight is two grams short of the expected result, then 2nd machine is producing defective coins.

For instance: if the weight of the coin is x, Then the expected result will be (1+2+....+10)x.

bibas100

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These questions are more for entry level workers. But, nevertheless, they are really challenging you to think and analyze- a great skill required in any job is the ability to think and analyze in a right way. You do not necessarily have to get the answer right in many questions like those below (of course, they expect you to get the answer to above questions right) but you got to show a logical deduction. A few that I know of:
1. How many street lamps are there in New York?
2. Estimate the market for light bulbs in Florida. (if you are into this field)

A lot of questions make use of algebra (simple) and logic.

Krishna Darlami

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Krishnaram ji,

That is great! That is the best way to find which machine is defective. Kudos to you.

Bibas100ji,

These question are not that vague like "How many street lamps in New York". There really is a mathematical deduction here.

ratobhaley

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2. What is the quickest way to get the sum of the numbers from 1 to 50?

Stiffler

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n(n+1)/2 = 50(50+1)/2 = 1275

ratobhaley

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stiffler let's say you didn't know the formula for it. I mean who goes to interview with all these formulas memorized. Could you do it in layman's terms?

nevermind

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1. 10 Degrees (at 3:15 the minute hand is at 90 deg and hour hand is at 100 deg) Well rough estimate.

2. if this is a dumb trick questions, then 'if you can weigh only once' means you can weigh only one coin once, weigh coins from each machine once, you will get the answer.

my 2 cents.

ratobhaley

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Nevermind some peeps have already answered both the questions and no the 2nd question is not a dumb trick question.

jhyalincha

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a) its a right angle-- all my clocks run 15 minutes late.

b) one of the machines is broke dude, just look for the 'defective machine' tag.

I am such a comedian. I should be on comedy central doing 'mind of jhyalincha'

parbatya

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Add 1+11+21+31+41 = 105
and 2+12+22+32+42 = 110
similarly
115
120
125
130
135
140
145
150
Now 10 x 100 = 1000
5x5 = 25
2x10+2x20+2x30+2x40+50=250
add together 1275

May be lengthy and you may have different solution

Chicago-Bull

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First, you calculate at home and then give ur answer "1275" while interviewing...so simple, dude! "ratera jaane kya"

Chicago-Bull

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A basket contains 5 apples. Do you know how to divide them to 5 kids so that each one has an apple and one apple stays in the basket??

ratobhaley

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Parbatya good try but its pretty lenghty. Easy way to do it is as follows Pair up the 1st number with the last number ie 1 and 50 which adds up to 51 Pair up 2nd and second from last ie 2 and 49 which adds up to 51 There are 25 such pairs from 1 to 50 so you multiply 51 times 25 to get your answer. In one step its 25 x 51 = 1275 Thanks for playing.

divdude

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give 4 apples to 4 kids and give the last kid apple with the basket.

dunno

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(n+1)/2 = 50(50+1)/2 = 1275
OR

Easy way to do it is as follows Pair up the 1st number with the last number ie 1 and 50 which adds up to 51 Pair up 2nd and second from last ie 2 and 49 which adds up to 51 There are 25 such pairs from 1 to 50 so you multiply 51 times 25 to get your answer. In one step its 25 x 51 = 1275 Thanks for playing.

what is the difference?

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