Prabhat remembers that his mother's birthday is after $17^{th}$ April but before $21^{st}$ April, whereas his sister Urmila remembers that their mother's birthday is after $19^{th}$ but before $24^{th}$ April. Which of the following days in April is definitely their mother's birthday ?
According to Prabhat Dates possible are 18,19, 20
According to Urmila Dates possible are 20, 21, 22, 23
hence common date is 20th . Hence option (D)