求一道简单的gmat数学。

先找出sample size: 2^4=16. 所以一共有16种可能, 分别是: GGGG, GGGB, GGBG, GGBB, GBGG, GBGB, GBBG, GBBB, BGGG, BGGB, BGBG, BGBB, BBGG, BBGB, BBBG, BBBB. B是BOY, G是GIRL. 所以如果是两男两女的机率就应该是6/16=3/8=0.375=37.5%. 希望对你有帮助.

百分之50

m:male, f:female
总共有5种情况：
mmmm, mfff, mmff, mmmf, ffff, ffmm
所以是20%

probability question...

1. first birth -have a boy - 1/2 (or 50%) probability
2. second child - have a boy - 1/2 (or 50%) probability
3. third child - have a girl - 1/2 (or 50%) probability
4. fourth child - have a girl - 1/2 (or50%) probability

multiply all of them

0.5*0.5*0.5*0.5 = 0.0625 = 6.25%

C2-1*C3-1/2**4=37.5%
C2-1为组合数2选1
C3-1为组合数3选1
2**4为2的四次方

20%