Life for grade-schoolers has changed a lot in just a few decades. While students growing up in the pre-digital age had to suffer through insanely difficult homework in silence, kids (and their parents) today can share their frustrations on the internet.

According to Over Sixty, the latest assignment to go viral comes from the parenting message board Mumsnet. After posting their 8-year-old child's math homework on a forum, user lucysmam quickly saw that the other parents were just as baffled by it. Here's the problem:

“On the coast there are three lighthouses. The first light shines for 3 seconds, then it is off for 3 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?”

Give up? The answer the parents came up with was 6 seconds for the first question and 120 seconds for the second one. The question becomes easier when you think of the lighthouses this way: The first one lights up every 6 seconds, the second one lights up every 8 seconds, and the third one lights up every 10 seconds. To calculate when all the lights will coincide, you need to find the lowest number divisible by six, eight, and 10, which comes out to 120.

When it comes to head-scratching elementary school lessons, this problem is just the start. If this viral problem is any indication, 6-year-olds have it even worse than 8-year-olds.

[h/t Over Sixty]