### 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?

### Crossing the Atlantic

Every day at noon a boat leaves Le Havre for New York while another boat leaves New York for Le Havre. The ocean crossing takes seven days. How many boats will each boat cross during their journey?

### On Time

On a clock the three hands - the second, minute and hour hands - are on the same axis. How often in a 24 hour day will the second hand be parallel to either of the two other hands?

# Bell Ringing

##### Age 11 to 14 Challenge Level:

We liked the solutions from Jake and Polly of West Flegg Middle School, Great Yarmouth.

NRICH can change to RNICH, RNCIH, RNIHC, NIRCH, NIRHC, NRCIH and NRIHC.
A peal of bells in which the 24 permutations of 4 bells are rung once each is given by
1234
2143
2413
4231
4321
3412
3142
1324
3124
1342
1432
4123
4213
2431
2341
3214
2314
3241
3421
4312
4132
1423
1243
2134
1234

For other solutions see the article Ding Dong Bell .