题目：一个数的\frac{2}{5}是20，这个数的\frac{3}{4}是多少?下面正确的列式是( ). 
选项：
bullet: A
text: 20× \frac{2}{5}÷ \frac{3}{4}
bullet: B
text: 20÷ \frac{2}{5}× \frac{3}{4}
bullet: C
text: 20÷ \frac{2}{5}÷ \frac{3}{4}
bullet: D
text: \frac{2}{5}÷ 20× \frac{3}{4}
答案：B
解析：20÷ \frac{2}{5}× \frac{3}{4} =50× \frac{3}{4} =\frac{75}{2} 答:这个数的\frac{3}{4}是\frac{75}{2}. 故选:B.