## 162. Math Puzzle $11 / 78$

Assume that a fly lays 120 eggs at the beginning of summer, on June 21st, and after 20 days, fully developed insects emerge from these eggs, each of which then lays 120 eggs. How many "descendants" would this fly have in total by the beginning of autumn?
Summer lasts 95 days. During this time, four generations of flies can lay their eggs:

| June 21 | 1 fly |
| :--- | ---: |
| after 20 days | 120 flies |
| after 40 days | 14400 flies |
| after 60 days | 1728000 flies |
| after 80 days | 207360000 flies |
| Total | 209102520 flies |

By the beginning of autumn, on September 23, the fly would theoretically have more than 209 million offspring.