Q 01/05

A 100 kg load of potatoes that is 99% water dries out until it is 98% water; what does it weigh now?

A) 50 kg

B) 90 kg

C) 98 kg

D) 99 kg

Answer · why

A) 50 kg

50 kg is all that remains: the 1 kg of solid potato must now be 2% of the load rather than 1%, so the total weight has to halve.

Q 02/05

In the film WarGames, which simple game does a computer play against itself to learn that nuclear war cannot be won?

A) Checkers

B) Hangman

C) Tic-tac-toe

D) Connect Four

Answer · why

C) Tic-tac-toe

Tic-tac-toe always ends level when both sides play perfectly, so the computer's endless draws teach it that some games have no winner.

Q 03/05

A drawer holds loose black socks and blue socks; without looking, how few must you pull to guarantee a matching pair?

A) Two

B) Three

C) Five

D) Twenty

Answer · why

B) Three

Three is enough: with only two colours, the third sock must match one of the first two, a rule mathematicians call the pigeonhole principle.

Q 04/05

How many people must gather in a room before it is more likely than not that two share a birthday?

A) 23

B) 57

C) 183

D) 366

Answer · why

A) 23

23 people are enough, because a group that size already contains 253 different pairs, and any one of those pairs could be the match.

Q 05/05

If 5 machines take 5 minutes to make 5 widgets, how many minutes would 100 machines need to make 100 widgets?

A) 1

B) 5

C) 20

D) 100

Answer · why

B) 5

5 minutes is right, because each machine takes five minutes to build one widget, so a hundred machines working side by side finish a hundred in the sa...