A homework puzzle aimed at eight-year-olds and featuring three lighthouses has left parents stumped - could you solve it?
The maths puzzle will challenge most adults, let alone primary school children, and there has been plenty of disagreement over the correct answer.
So if SATs and GCSEs this week haven't got you tearing your hair out, you can pit yourself against Year Four pupils by trying to solve the homework riddle.
Branded "ridiculous" by mums and dads , the question focuses on common multiples, reports The Mirror .
So could you solve it?
"On the coast there are three lighthouses.
"The first light shines for 3 seconds then it is off for three seconds.
"The second light shines for 4 seconds then it is off for 4 seconds.
"The third light shines for 5 seconds then it is off for 5 seconds. All three lights have just come on together.
"When is the first time that all three of the lights will be off together?
"When is the next time that all three lights will come on at exactly the same moment?"
However one parent think they've managed to crack it, and their working shows the problem could be solved by writing out every time they were off and then finding out when they were off at the same time.
So, the first light comes on every 6 seconds, the second every 8, the third every 10.
The next step is working out the lowest number that can be divided by all those numbers which is apparently 120.
Which we would have never worked out for ourselves in a million years.