Answer:
The probability of choosing 2 girls from a list of 6 girls and 6 boys can be calculated using combinations.
The number of combinations of choosing 2 girls out of 6 girls is given by the formula: C(6,2) = 6! / (6-2)!2! = 15.
So, the probability of choosing 2 girls is 15 / (C(12,2) = 66) = 15/66 = 5/22.
Therefore, the probability of Mr. Mackinson choosing 2 girls to lead the class field trip is 5/22 or approximately 0.227.