If a sprinkler waters 1 over 12 of a lawn in 1 over 4 hour, how much time will it take to water the entire lawn?

I believe it would be 3 hours!

That is right Alex but it would be good if you discussed it a little.

We are here to teach people - not just to give answers :)

the entire lawn is 12 times bigger than what was mowed in a $${\frac{{\mathtt{1}}}{{\mathtt{4}}}}$$   of an  hour.

so

the entire lawn will take     $${\mathtt{12}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{4}}}}\right)$$ hours to mow    :)))