It is important to know that July has 31 in total.
The probability of being born in July is
![P=(1)/(12)](https://img.qammunity.org/2023/formulas/mathematics/college/odhaigbk7ufeok5xkjjobp98vir8xb5to4.png)
The probability of being born on a day that is multiple of 3 is
![P=(9)/(31)](https://img.qammunity.org/2023/formulas/mathematics/college/gsgs1upaspt30yxl592gptexgdxa5trizr.png)
Because there are 9 days which are multiple of 3.
Then, we sum both probabilities.
![P=(1)/(12)+(9)/(31)=(31+108)/(372)=(139)/(372)\approx0.37](https://img.qammunity.org/2023/formulas/mathematics/college/i4qld7jwk4hilxjx71an4eof09bnd6twf5.png)
Hence, the probability is 0.37, or 37%, approximately.