$\frac{6!}{3!\times2!}=60$. 
How many distinguishable arrangements are there of $1$ blue tile, $2$ green tiles, and $3$ yellow tiles in row from left to right? (Tiles of the same color are indistinguishable) 
Options:
1) $$12$$ 
2) $$18$$ 
3) $$24$$ 
4) $$30$$ 
5) $$60$$ 