Parents are baffled by this primary school maths puzzle

omg 14/05/2018

A mum has taken to Mumsnet for help after failing to crack a puzzle that her young daughter brought home from primary school.

Many people have struggled with the puzzle, but can you crack it?

The full puzzle is below...

"On the coast there are 3 lighthouses.

The first light shines for 3 seconds, then is off for 3 seconds.

The second light shines for 4 seconds, then is off for 4 seconds.

The third light shines for 5 seconds, then is off for 5 seconds.

All three lights have just come on together.

1) When is the first time all three lights will be off together?

2) When is the next time all three lights will come on at the same moment?"


Question 1: The first time all lights will be off is after 5 seconds

Question 2: To figure out when all 3 lights will next be on at the same time, you need to work out the lowest common denominator of 6, 8 and 10 - which is 120 secs.

Did you manage to crack the puzzle correctly?