7.4. In grandmother's garden, apples have ripened: Antonovka, Grushovka, and White Naliv. If there were three times as many Antonovka apples, the total number of apples would increase by $70 \%$. If there were three times as many Grushovka apples, it would increase by $50 \%$. By what percentage would the total number of apples change if there were three times as many White Naliv apples?
Answer: increased by $80 \%$.

Solution. First method. If the amount of each type of apple were three times as much, the total number of apples would increase by $200 \%$. Of this, $70 \%$ is due to the increase in Antonovka, and $50 \%$ is due to the increase in Grushovka. Therefore, the increase due to White Naliv would be $200 \%-70 \%-50 \%=80 \%$.

Second method. Since adding twice the amount of Antonovka results in a $70 \%$ increase, Antonovka makes up 0.35 of all apples. Similarly, Grushovka makes up 0.25 of all apples. Therefore, the share of White Naliv is 0.4. If you add 0.4 twice to a number, the number will increase by $80 \%$.

Grading criteria.

“+” A complete and justified solution is provided

“士” A correct reasoning is provided, but a computational error is made

“Ғ” Only the correct answer is provided or it is obtained by considering a specific example

“-” The problem is not solved or is solved incorrectly