Puzzles in Interviews

This post is all about puzzles asked in actual interviews.

1.      3 Bulbs 3 Switches Problem:

There is a room with door (closed) and 3 light bulbs. Outside the room, there are 3 switches, connected to the bulbs. You may manipulate the switches as you wish. But once you open the door, you can't change them. Identify each switch with it's bulb.

Answer:  Turn on 1 switch and keep it on for 5 minutes. Now turn off it and turn on 2^nd switch and enter the room. Now, the on bulb maps to on switch. The hot bulb maps to previous on switch and 3^rd bulb maps to 3^rd switch.

2.      You have 8 balls. One of the balls weighs less than others. You have a balance to measure balls against each other. In 2 weighings find the defective one?

Answer:  First , put  2 balls aside. And put 3-3 balls on each side of weighing scale. If these are equals, then just find 1 ball from remaining 2 balls. If these are not equal, then take 3 balls which are light and put 1 ball aside and put 2 balls [1-1] on each side of weighing scale. If these are equal, then the bal kept aside is the ball with less weight. Else if these are not equal, then light ball is easily found.

3.      Cut a cake into 8 pieces with 3 cuts.

Answer: Cut the cake in 2 halves. Put one half over another and cut again in plus sign. We get 8 pieces.

4.      Why is a manhole cover round?

Answer:  Round ones can be carried easily using rotating.

And round ones can be fitted in hole easily, whereas square ones need matching the sides.

5.      If you have three, you have three. If you have two, you have two but if you have one, you have none. What is it?

Answer: Choices

6.      Balance the equation 101 – 102 = 1 by putting some operators in it?

Answer: -(101-102)

7.      How many basketballs would fit in this room?

Answer: 2, becoz, ROOM has 2 O’s , so only 2 balls will fit.

8.      How many degrees (if any) are there in the angle between the hour and minute hands of a clock when the time is a quarter past three?

Answer: 7.5 degree

9.      Burning Sticks: You have two sticks and matchbox. Each stick takes exactly an hour to burn from one end to the other. The sticks are not identical and do not burn at a constant rate. As a result, two equal lengths of the stick would not necessarily burn in the same amount of time.  How would you measure exactly 45 minutes by burning these sticks?

Answer:

0 minutes – Light stick 1 on both sides and stick 2 on one side.
30 minutes – Stick 1 will be burnt out. Light the other end of stick 2.
45 minutes – Stick 2 will be burnt out.

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