# Silicon Valley's Top Engineers Can Answer These 7 Ridiculous Riddles

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Some of the top technology firms in Silicon Valley — Google, Apple, Facebook and others — have very strenuous hiring processes.Often times, that requires asking very weird brain teasers to test the logical abilities of each prospective engineer.

We’ve gathered a new group of these questions (and answers) from MyCareerStacks, which vary from multiple companies.

If you want to prepare for an interview at Google or any other major tech firm, or just see if you have what it takes, you should test yourself with these questions. They will probably pop up in some form during the recruiting process.

### You have 50 bikes with a tank that have the capacity to go 100 kilometers...

Using these 50 bikes, how far can you go?

### ANSWER: You'll have to move around gasoline!

The simplest, naive answer is to make them all move at once and move 100 kilometers.

However there's another solution!

Take all the bikes 50 kilometers first. Then, take all the gas from half the bikes, and pour them into the other half. You now have 25 bikes with full tanks.

Then travel another 50 kilometers, and repeat. This way, you can travel 350 kilometers total.

For extra credit, there was a little bit of rounding concerning an extra bike from the 25 to 12 bike step. You can travel even further with that gas!

### You are on a boat, and throw out a suitcase...

Does the water level increase?

Company: Microsoft

While the briefcase is in the boat, it displaces its weight in water.

If it's heaver than water when you toss it in, it'll displace its volume in the water. If it's lighter, it will still displace its weight.

In no case will the water level actually increase!

### You're given a pair of tic-tac-toe boards...

Find a way to determine, when rotated, that they are the same board.

Company: Microsoft

### ANSWER: There are 7 other conditions to check.

With your tic-tac-toe boards, you can rotate them left or right four times, and then mirror it and do the same again.

So, the way to do this is to reduce it down to a matrix and then rotate it, one step at a time, to check if it matches another board.

Mathematically, the way to do this is to turn it into a three-by-three matrix, and then flip the rows and columns. If you want to rotate it to the right, switch the columns, and to rotate it left, switch the rows.

### You have an infinite supply of water...

... and you also have a 5 liter bucket and a 3 liter bucket. How do you measure four litres?

Company: Microsoft

### ANSWER: Start by filling the five-liter bucket...

... and pour that into the three-liter bucket. Now you have 2 litres in the big bucket and 3 in the little one.

Empty the little bucket, and pour the last 2 litres from the big bucket into the little bucket.

Fill the big bucket, and then use that water to fill up the little bucket. Since the little bucket already has 2 litres, it will fill up by 1 liter, leaving the big bucket with four litres.

### You toss two coins...

If you get heads with the first coin, you stop. If you get tails, you toss it again. The second coin is tossed regardless.

What is the ratio of heads to tails?

Company: Amazon

### ANSWER: It's still one to one.

Since you're only expected to toss the first coin twice -- given a 50/50 chance of getting heads -- the ratio is 1 to 1.

The second coin is also continuously tossed, and has a ratio of 1 to 1.

So, the whole ratio is still 1 to 1.

### You are given two dice...

One is normal, and one is blank. How do you number the second dice, so you have an equal chance of getting any number?

### Answer: Just use zeroes and sixes.

If you throw two dice that are both numbered 1 to 6, then there's a higher chance of some numbers to appear.

So if you paint the second dice with three zeroes and three sixes, you have a 1 out of 2 chance of getting either a 0 or a 6.

The probability of getting any number between 1 and 6 is basically 1 out of 2 chance of getting a zero on the painted dice, and 1 out of 6 on the normal dice -- so one out of 12.

The same is true for a number from 7 to 12 -- one out of 12.

So you have a one out of 12 chance of getting any number from 1 to 12.

### You have 1,000 bottles of juice...

One contains poison and tastes bitter. How do you find it in the smallest number of sips?

Company: Microsoft

Take one drop from 500 of the bottles, and take a sip.

If it tastes bitter, it's in one of those 500 bottles.

Then do the same for 250 bottles, then 125 bottles, and so on and so forth...

Until you find the exact bottle that's the poison.