明知小学六年级一班男生的人数占全班总人数的70%，六年级二班的男生比一班男生少2名，而女生人数为一班女生的2倍．如果两班合在一起，则男生所占的比例为60%．请问：二班有多少名女

Answer 1

设二班有x名女生，则一班有女生0.5x名，
可得一班的总人数是0.5x÷（1-70%），
所以一班的男生人数是0.5x÷（1-70%）×70%，
二班的男生人数是0.5x÷（1-70%）×70%-2；
因为两班合在一起，则男生所占的比例为60%，
可得男、女生的人数比是60%：（1-60%）=3：2，
则[0.5x÷（1-70%）×70%×2-2]：（x+0.5x）=3：2，
                       （(7)/(3)x-2）：（(3)/(2)x）=3：2
                                  (14)/(3)x-4=(3)/(2)x×3
                                     (x)/(6)＝4
                                  (x)/(6)×6＝4×6
                                      x=24
答：二班有24名女生． (7)/(3)777333x-2）：（(3)/(2)x）=3：2
                                  (14)/(3)x-4=(3)/(2)x×3
                                     (x)/(6)＝4
                                  (x)/(6)×6＝4×6
                                      x=24
答：二班有24名女生． (3)/(2)333222x）=3：2
                                  (14)/(3)x-4=(3)/(2)x×3
                                     (x)/(6)＝4
                                  (x)/(6)×6＝4×6
                                      x=24
答：二班有24名女生． (14)/(3)141414333x-4=(3)/(2)x×3
                                     (x)/(6)＝4
                                  (x)/(6)×6＝4×6
                                      x=24
答：二班有24名女生． (3)/(2)333222x×3
                                     (x)/(6)＝4
                                  (x)/(6)×6＝4×6
                                      x=24
答：二班有24名女生． (x)/(6)xxx666＝4
                                  (x)/(6)×6＝4×6
                                      x=24
答：二班有24名女生． (x)/(6)xxx666×6＝4×6
                                      x=24
答：二班有24名女生．