Answer:
1845
Step-by-step explanation:
if one of the prefects must be a girl, the only allowed combinations are GBB, GGB, and GGG
GBB
(15c2 * 10c1) / 25c3 = 21/46
GGB
(15c1 * 10c2) / 25c3 = 27/92
GGG
(15c0 * 10c3) / 25c3 = 6 / 115
21/46 + 27/92 + 6 / 115 = 369 / 460 or 0.802...
25c3 = 2300 * 0.802... = 1845
