### Rule of Three

If it takes four men one day to build a wall, how long does it take 60,000 men to build a similar wall?

### Square Pegs

Which is a better fit, a square peg in a round hole or a round peg in a square hole?

### How Big?

If the sides of the triangle in the diagram are 3, 4 and 5, what is the area of the shaded square?

# Washing Elephants

##### Age 11 to 14 ShortChallenge Level

Answer: 22$\frac29$ minutes

Scaling up to more elephants
Mary: 50 minutes   1 elephant          200 minutes   4 elephants

Nigel: 40 minutes   1 elephant          200 minutes   5 elephants

Together:  200 minutes    9 elephants
200$\div$9 minutes  1 elephant
200$\div$9 = 22$\frac29$

Seeing how much of the elephant is clean after 10 minutes (or 5, or 20, etc)
Mary:  50 minutes   1 elephant            10 minutes   $\frac15$ elephant

Nigel:  40 minutes   1 elephant            10 minutes   $\frac14$ elephant

Together:                                            10 minutes   $\frac15+\frac14=\frac9{20}$ elephant
10$\div$9 minutes    $\frac1{20}$ elephant
200$\div$9 minutes    1 elephant
200$\div$9 = 22$\frac29$

You can find more short problems, arranged by curriculum topic, in our short problems collection.