A couple uses periodic abstinence as the textbook describes it: they avoid coitus on days 10 to 17…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A couple uses periodic abstinence as the textbook describes it: they avoid coitus on days to of the menstrual cycle, counting from the first day of bleeding. The cycle of the woman is days long. Use the model of the lesson. In the model, ovulation comes days before the next period starts, and the fertile days run from days before ovulation to days after it.
- On which day does ovulation come?
- Which days are the fertile days of the model? Give the first and the last.
- How many fertile days of the model fall outside the days to ?
- What does this show about the method?
Need a reminder? The key ideaShow
Periodic abstinence avoids coitus on days to of a cycle of days. In the model, ovulation is days before the next period, and the fertile days run from days before ovulation to days after it. Condoms are used once, and they also protect against STIs. An IUD is placed by a trained person. Copper ions reduce the movement of sperms.
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.
Given. Cycle: days. Days of abstinence: to .
Plan. Find the day of ovulation, the fertile window, and then count the days that are not covered.
Step 1. Ovulation. , so ovulation is on day .
Step 2. The fertile days. and . The window is days to , which is days.
Step 3. The days not covered. Days to fall inside the days of abstinence. Days , , and fall outside. That is days.
Step 4. The meaning. Half of the fertile window is left uncovered. The method cannot be relied on when the cycle is not days long.
Answer: day ; days to ; days; the method often fails.
Check. For a cycle of days, the same steps give days to , so the model agrees with the textbook there.
Watch out. The model is a way to learn the idea. It is not a method to use, and a doctor should be asked about planning a family.
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