66. Two beetles crawl from point $A$ to point $B$ and return back. The first beetle crawls both ways at the same speed. The second beetle crawls to $B$ 1.5 times faster than the first, but returns 1.5 times slower than the first. Which beetle returned to $A$ first?
66. Let's write the condition of the problem in the form of a table:

|  | speed |  | path |  | time |  |
| :---: | :---: | :---: | :---: | :---: | :---: | :---: |
|  | there | back | there | back | there | back |
| 1st beetle | $v$ | $v$ | $s$ | $s$ | $s / v$ | $s / v$ |
| 2nd beetle | $3 v / 2$ | $2 v / 3$ | $s$ | $s$ | $2 s / 3 v$ | $3 s / 2 v$ |

The first beetle spent the total time $t_{1}=\frac{2 s}{v}=\frac{12 s}{6 v}$, while the second beetle spent the time $t_{2}=\frac{2 s}{3 v}+\frac{3 s}{2 v}=\frac{13 s}{6 v} ; t_{1}<t_{2}$, therefore, the first beetle returned earlier.