There were 18 students assigned for the field trip.
Eight of these students were boys, so the remaining students are girls.
Therefore, there were 18 - 8 = 10 girls assigned for the field trip.
On the day of the field trip, the number of girls and boys was the same.
This means that there were 8 boys and 8 girls present for the field trip.
So, the number of girls not able to join the field trip is 10 - 8 = 2.
#### 2
The answer is: 2
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
There were 18 students assigned in a minibus for a field trip. Eight of these students were boys. On the day of the field trip, the number of girls and boys was the same since some of the girls were not able to join the trip. How many girls were not able to join the field trip?

### Answer:
