Problem 5. On 6 trees there are 129 birds. At one moment, 6 birds flew away from the first tree, 11 from the second, 8 from the third, 10 from the fourth, 7 from the fifth, and 9 from the sixth. Then on all the trees, the same number of birds remained. How many birds were there on each tree at the beginning?
Solution. When the birds flew away from the six trees, the remaining

$$
129-(6+11+8+10+7+9)=129-51=78
$$

On all the trees, the same number of birds remained, so 78:6=13. On each tree, 13 birds remained. At the beginning, on the first tree, there were $13+6=19$ birds, on the second $13+11=24$, on the third $13+8=21$, on the fourth $13+10=23$, on the fifth $13+7=20$, and on the sixth tree $13+9=22$.

## V section