1The idea that aliens built the pyramids is ludicrous and has no scientific basis.
2Is it ludicrous to think that we can solve climate change in just a decade?
3He made a ludicrous claim that he could run a marathon in under two hours.
4If you think that's a good plan, I think you're being ludicrous.
5The plot of the movie was so ludicrous that it became entertaining in its own right.