Why did you only need to flip the male parent coin to determine the sex of your smiley face?

Only male parent coin is flipped to determine the sex of your smiley face because:

A pair of X chromosomes is present in female, it contributes one X, and a pair of XY chromosome in male. So in order to determines if the smiley will be female or male. The male coin is needed to be flipped. The chromosome can only be determined only when the sperm fertilises the egg. In mother egg all the gametes have X chromosome, but the sperm has X and Y chromosome. If the sperm carry X chromosome, their will be female. If it carries Y chromosome then it will be male.