Brain Teaser

Question 1

Boat with a lot. What happens if you drop the lot in the water?

Answer 1

Water level falls as the density of a lot is higher than the water

Question 2

How many golf balls can you fit in an airplane?

Answer 2

Important thing here is methodology: Take out seats? Cones in the end?, measurements?

Question 3

What is highest 30% of 17 or 17% of 30

Answer 3

Same same

Question 4

You are given 12 balls and a scale. Of the 12 balls, 11 are identical and 1 weighs EITHER slightly more or less. How do you find the ball that is different using the scale only three times AND tell if it is heavier or lighter than the others?

Answer 4

4 & 4 -> 2&2 -> 1&1

Question 5

What is the sum of all the numbers 1 to 100?

Answer 5

The trick here is that you have 50 pairs which each sum to 101 (e.g. 1+100, 2+99, 3+98, etc.). So, 50 times 101 = 5050.

Question 6

There are 3,182 players in a tennis head-to-head knockout tennis tournament. How many matches must be played to crown a winner?

Answer 6

3181

Question 7

How many times a day do a clock’s hands overlap?

Answer 7

22

Question 8

There are three boxes of eggs. In each box is either big eggs, small eggs or big and small eggs. The boxes are labelled “big,” “small,” and “mixed,” but every box mislabeled. What is the least number of boxes you can open to know which eggs are in which box?

Answer 8

1

Question 9

You are blindfolded and sit in front of a table. On the table is a large number of coins, 10 of which have heads facing up. How do you split the group of coins into two groups such that the same number of coins are heads-up in each group? Note: You don’t know how many coins there are and you can’t tell which side is facing up in any way.

Answer 9

Separate 10 of the coins from the group and put them to one side and turn all of the coins in the group of 10 on to their opposite sides

Question 10

It’s 3:30pm. What is the angle formed by the hour hand and the minute hand?

Answer 10

75 degrees

Question 11

McNuggets come in boxes of 6, 9, and 20. What is the largest number of nuggets that it is not possible to obtain by purchasing some combination of these boxes?

Answer 11

43

Question 12

You own a pet store. If you put in one canary per cage, you have one canary too many. If you put in two canaries per cage, you have one cage too many. How many canaries and cages do you have?

Answer 12

4 canaries and 3 cages

Question 13

A man leaves home for a mountain at 1pm and reaches the top at 3pm. The following day he departs from the top at 1pm and gets home at 3pm, by following the same path as the day before. Was he necessarily ever at the same point on the path at the same time on both days?

Answer 13

Yes

Question 14

You drive to the store at 20 mph and return by the same route at 30 mph. Discounting the time spent at the store, what was your average speed?

Answer 14

24 mph

Question 15

Monty Hall Problem – 3 konvolutter

Answer 15

Always switch, odds increases from 1/3 to 2/3

Question 16

A windowless room has 3 lightbulbs. You are outside the room with 3 switches, each controlling one of the lightbulbs. If you can only enter the room one time, how can you determine which switch controls which lightbulb?

Answer 16

Turn on two switches (call them A and B) on and leave them on for a few minutes. Then turn one of them off (switch B) and enter the room. The bulb that is lit is controlled by switch A. Touch the other two bulbs (they should be off). The one that is still warm is controlled by switch B. The third bulb (off and cold) is controlled by switch C.

Question 17

A car travels a distance of 60 miles at an average speed of 30 mph. How fast would the car have to travel the same 60 mile distance home to average 60 mph over the entire trip?

Answer 17

Most people say 90 mph but this is actually a trick question! The first leg of the trip covers 60 miles at an average speed of 30 mph. So, this means the car traveled for 2 hours (60/30). In order for the car to average 60 mph over 120 miles, it would have to travel for exactly 2 hours (120/60). Since the car has already traveled for 2 hours, it is impossible for it to average 60 mph over the entire trip.

Question 18

You’ve got a 10 x 10 x 10 cube made up of 1 x 1 x 1 smaller cubes. The outside of the larger cube is completely painted red. On how many of the smaller cubes is there any red paint?

Answer 18

First, note that the larger cube is made up of 1000 smaller cubes. The easiest way to think about this is how many cubes are NOT painted? 8 x 8 x 8 inner cubes are not painted which equals 512 cubes. Therefore, 1000 – 512 = 488 cubes that have some paint. Alternatively, we can calculate this by saying that two 10 x 10 sides are painted (200) plus two 10 x 8 sides (160) plus two 8 x 8 sides (128). 200 + 160 + 128 = 488.

Question 19

You are given a 3-gallon jug and a 5-gallon jug. How do you use them to get 4 gallons of liquid?

Answer 19

Fill the 5-gallon jug completely. Pour the contents of the 5-gallon jug into the 3-gallon jug, leaving 2 gallons of liquid in the 5-gallon jug. Next, dump out the contents of the 3-gallon jug and pour the contents of the 5-gallon jug into the 3-gallon jug. At this point, there are 2 gallons in the 3-gallon jug. Fill up the 5-gallon jug and then pour the contents of the 5-gallon jug into the 3-gallon jug until the 3-gallon jug is full. You will have poured 1 gallon, leaving 4 gallons in the 5-gallon jug.

Question 20

What is 49 x 63?

Answer 20

The best way is to use easy numbers. 49 x 63 is in reality equal to 50 x 63 minus 63. 50 x 63 = 100 x 63 / 2 = 6,300/2 = 3,150. Deduct 63 from 3,150 = 3,087. You can use this “breakdown” method for almost every calculation

Question 21

How many cuts do I need to get exactly 16 equally-sized slices of pizza?

Answer 21

8 cuts

Question 22

Four investment bankers need to cross a bridge at night to get to a meeting. They have only one flashlight and 17 minutes to get there. The bridge must be crossed with the flashlight and can only support two bankers at a time. The Analyst can cross in 1 minute, the Associate can cross in 2 minutes, the VP can cross in 5 minutes and the MD takes 10 minutes to cross. How can they all make it to the meeting in time?

Answer 22

First, the Analyst takes the flashlight and crosses the bridge with the Associate. This takes 2 minutes. The Analyst then returns across the bridge with the flashlight taking 1 more minute (3 minutes passed so far). The Analyst gives the flashlight to the VP and the VP and MD cross together taking 10 minutes (13 minutes passed so far). The VP gives the flashlight to the Associate, who recrosses the bridge taking 2 minutes (15 minutes passed so far). The Analyst and Associate now cross the bridge together taking 2 more minutes. Now, all are across the bridge at the meeting in exactly 17 minutes.

Question 23

“In the middle of a pond is a single lily pad; the lily pad doubles in size every day and the pond is completely covered on the last day of the month (30 days). How long does it take for the pond to be half covered?”

Answer 23

Answer: 29 days because, if it doubles in size each day it also halves each day. Thus at 29 days is half full in order to be completely full in 30 days.

Question 24

How many hairstylists or barbers do you estimate there are there in this city? Explain your logic/assumptions.”

Answer 24

Answer: Explain the logic based on the population of the city, average number of cuts people have per year, number of cuts one barber can do per year, and thus how many that implies there must be. (e.g., 2 million people, each get an average of 4 cuts per year, which results in 8 million cuts per year. Each barber works an average of 8 hours per day, times five days per week, times fifty weeks per year equals 2,000 hours of cutting time per year. Each haircut takes 1 hour. Thus, 8 million haircuts, equal 8 million hours, divided by 2,000 hours per barber requires 4,000 barbers in the city.)