All boys are regarded as 1, and the boys participating in the competition are111.

The rest of the boys are all boys:1-11=10/1.

This figure is twice that of the remaining girls, indicating that the remaining girls are all boys: (1011)/2 = 5/11.

So the rest of the girls and all the boys are boys: 5/11+0 =16/1,

This number is:156-12 =144 (person)

The number of all boys is 16/ 1 1 multiplied by 144. The number of all boys is144/(16/11) = 99 (people).

All female students are: 156-99=57 (persons).

Checking calculation: 57- 12=45 for girls, 99 *10/1= 90 for boys/girls = 90/45 = 2 (times), which is in line with the meaning of the question.