*For more help preparing for interviews visit our interview advice section.*

Having heard from friends and read online about some of the challenging (and sometimes ridiculous) interview questions you get asked at Google, we thought we’d put together a list of challenging/entertaining questions candidates have been asked at the Googleplex.

Be warned, these may make your brain hurt a little bit! It’s also worth noting that these questions are usually reserved for technical candidates, so if you’re going for a marketing or account management role at Google, you probably won’t get any of these!

# The 8 toughest Google Job Interview questions

- Explain a database in 3 sentences to your 7 year old nephew.
- How many golf balls could you fit into a classic American school bus?
- How many petrol stations are there in the USA?
- How much should you charge to wash all the windows in Seattle?
- What is the probability of breaking a stick into 3 pieces and forming a triangle?
- Why are manhole covers round?
- You are shrunk to the height of a 10p piece and your weight is proportionally reduced so as to maintain your original density. You are then thrown into an empty glass blender. The blades will start moving in 60 seconds. What do you do?”
- You are at a party with a friend and 10 people are present including you and the friend. Your friend makes you a wager that for every person you find that has the same birthday as you, you get £1; For every person that does not have the same birthday as you, he gets £2. Would you accept the wager?

### 1. Explain a database in 3 sentences to your 7 year old nephew.

*Answer – A database is a way of organizing information. It’s like a genie who knows where every toy in your room is. Instead of hunting for certain toys yourself and searching the whole room, you can ask the genie to find all your toy soldiers, or only X-Men action figures, or only race cars — anything you want.*

### 2. How many golf balls could you fit into a classic American school bus?

*Answer – the density of a closest packing for spheres is pi/sqrt(12) or .9069. *

*1/.9069 = 1.1027 volume occupied by spheres in a given space.*

*Further with all the material in a school bus, it can be treated as a cylinder with a radius of 4 feet or 48 inches and a length of 22 feet or 264 inches. (pi(r)^2)h is the volume of a cylinder. The total volume is 401,420 cubic inches. The diameter of the ball is 1.6 and is enclosed by a cube with volume = 4.096. 401,420/4.096= 98,001*

*This is then multiplied by the density and the answer is 88,877 balls*.

### 3. How many petrol stations are there in the USA?

*Answer – A business doesn’t stick around for long unless it makes a profit. Let’s assume that all gas stations in the US are making at least some profit over the long run. Assume that the number of people who own more than one car is negligibly small relative to the total American population. Figure that 20% of people are too young to drive a car, another 10% can’t drive because of disability or old age, 5% of people use public transportation or carpool, another 5% choose not to drive, and another 5% of the cars are inventory sitting in lots or warehouses that a dealership owns but which no one drives.*

* There’s about 280 million people in the US; subtracting 50%, that means there’s about 140 million automobiles and 140 million drivers for them. The busiest city or interstate gas stations probably get a customer pulling in about twice a minute, or about 120 customers per hour; a slower gas station out in an agrarian area probably sees a customer once every 10 or 15 minutes, or about 4 customers per hour. Let’s take a weighted average and suppose there’s about one customer every 90 seconds, or about 40 customers an hour. Figuring a fourteen-hour business day (staying open from 7 AM to 9 PM), that’s about 560 customers a day.*

* If the average gas station services 560 customers a day, then there are 250,000 gas stations in the US. This number slightly overstates the true number of gas stations because some people are serviced by more than one gas station. [Actual number in 2003, according to the Journal of Petroleum Marketing: 237,284, an error of about 5%.]*

### 4. How much should you charge to wash all the windows in Seattle?

*Answer – Assuming 10,000 city blocks, 600 windows per block, five minutes per window, and a rate of $20 per hour, about $10 million*

### 5. What is the probability of breaking a stick into 3 pieces and forming a triangle?

*Answer – The answer is complicated (and long). For the geeks among you, check out this link for the mathematical explanation.*

### 6. Why are manhole covers round?

Answer – A round manhole cover cannot fall into the hole it covers. In addition, heavy, round manhole covers are easier for one person to move by standing it on end and rolling. Also, you don’t have to “align” a manhole cover to it’s hole. Any orientation will do.

### 7. You are shrunk to the height of a 10p piece and your weight is proportionally reduced so as to maintain your original density. You are then thrown into an empty glass blender. The blades will start moving in 60 seconds. What do you do?”

*Answer – (well, a genuine answer given by a candidate) – Take off all my clothes, wedge them between the blades and the floor to prevent it from turning. Back up against the edge of the blender until the electric motor overheats and burns out. Using the notches etched in the side for measuring, climb out. If there are no such notches or they’re too far apart, retrieve clothes and make a rope to hurl myself out.*

### 8. You are at a party with a friend and 10 people are present including you and the friend. Your friend makes you a wager that for every person you find that has the same birthday as you, you get £1; For every person that does not have the same birthday as you, he gets £2. Would you accept the wager?

*Answer – My expected Profit = 1*(1/365)+2*(1/365)^2+3*(1/365)^3+…+10*(1/365)^10 = 1 (approx)*

*The above expression is AGP. Refer the formula for*

*sum of n terms*

*Friend’s expected profit = 2*(364/365) + 4*(364/365)^2 + .. + 20*(364/365)^10 = -18*365 (approx)*

*My profit (+ve) > My friend profit (-ve)*

*Hence I accept the bet.*