The number of 4 digit numbers without repetition that can be formed using the digits 1, 2, 3, 4, 5, 6, 7 in which each number has two odd digits and two even digits is
Given digits are 1, 2, 3, 4, 5, 6, 7. Two even digits can be selected in $^{3}C_{2}$ Two odd digits can be selected in $^{4}C_{2}$ ways. These selected 4 digits can be arranged in 4! ways. $\therefore\, Total \,number\, of \,ways=^{4}C_{2}. ^{3}C_{2}. 4!$ $=6\times3\times24$ $=18\times24$ $=432$