(1) solution: because the number of male teachers accounts for 2 out of 7, and the number of female teachers accounts for 5 out of 7.

Five sevenths of 42 equals 30.

(2) Because the number of math, Chinese and English teachers is 4:5:5.

The math teacher is 42 times 65438+4/04 equals 12.

For Chinese teachers, 42 of 04 times 65438+5 is equal to 15.

For English teachers, 42 times 65438+5/04 equals 15.

(3) Let there be a female teacher and a 4a male teacher.

Because at this time, the number of female teachers is twice that of male teachers.

So 30+a=2( 12+4-a)

a=

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