I am quite sure your teacher is expecting
you to give 1/2, 0.5, or 50% for both answers.
However, from this website:
http://www.scientificamerican.com/article/is-a-pregnant-womans-chan/
Marc Weisskopf, a research associate at the Harvard School
of Public Health, says:
In most industrialized countries about 105 boys are born
for every 100 girls, for a ratio of 1.05, known as the
secondary sex ratio, or SSR; the primary sex ratio is the
ratio at conception. This is often expressed as the
percentage of boys among all births, or about 51.2 percent.
So even though your teacher is expecting answers
1/2, 0.5, or 50% for each,
If Weisskopf is right, the answer to (a) should be
(a) 64/125 or 0.512 or 51.2%
and the answer to (b) should be
(b) 61/125 or 0.488 or 48.8%
Edwin
