List every possible family of three children in order of birth, writing G for a girl and B for a…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
List every possible family of three children in order of birth, writing G for a girl and B for a boy. How many families are there? In how many is there exactly two girls? Give the chance of exactly two girls as a fraction.
Need a reminder? The key ideaShow
In some reptiles the temperature of the eggs decides the sex, and some snails change sex. Human women are XX and men are XY. Every egg carries X; half the sperm carry X and half Y. An X sperm gives a girl, a Y sperm a boy, with an equal chance each time.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. All families. : GGG, GGB, GBG, GBB, BGG, BGB, BBG, BBB.
Step 2. Two girls. GGB, GBG and BGG, which is .
Step 3. The chance. .
Answer: families; have exactly two girls, a chance of .
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