Answer: The required probability is 65.26%.
Step-by-step explanation: Given that two students form a group of eight boys and 12 girls are sent to represent the school in a parade.
We are to find the probability that the students chosen are not both girls, if the two students are chosen at random.
Total number of students in the group = 8 + 12 = 20.
Let S denote the sample space for the experiment of selecting two students and A denote the event that both the students are not girls.
Then,
![n(S)\\\\=^(20)C_2\\\\\\=(20!)/(2!(20-2)!)\\\\\\=(20*19*18!)/(2*1*18!)\\\\=190,\\\\\\\\n(A)\\\\\\=^8C_2*^(12)C_0+^8C_1*^(12)C_1\\\\\\=(8!)/(2!(8-2)!)*1+8*12\\\\\\=28+96\\\\=124.](https://img.qammunity.org/2019/formulas/mathematics/high-school/bcl5d1iwthr03bm02txjlbnhrm5ltrovom.png)
Therefore, the probability of event A is given by
![P(A)=(n(A))/(n(S))=(124)/(190)=(62)/(95)*100\%=65.26\%.](https://img.qammunity.org/2019/formulas/mathematics/high-school/harxyul2ylo7gtl5v94vxfp4frf15nwure.png)
Thus, the required probability is 65.26%.