[ Systems of linear equations ] [ Arithmetic. Mental calculation, etc. ]

At the bottom of the lake, springs are bubbling. A herd of 183 elephants could drink the lake dry in 1 day, while a herd of 37 elephants could do it in 5 days.

How many days would it take for one elephant to drink the lake dry?
37 elephants over five days drink as much as $37 \cdot 5=185$ elephants in one day. The difference of two elephants is explained by the fact that over the extra four days, the springs "fill up" with as much water as two elephants drink in a day. Thus, the springs replenish half of an elephant's daily portion each day. And in the lake (without the springs), there are 182.5 daily portions for an elephant. One elephant drinks water "from the lake" for half the day, and "from the springs" for the other half. Therefore, it will take $182.5 \cdot 2=365$ days.

## Answer

It will take 365 days.