Researchers measured the heart rates of several randomly selected astronauts exercising on stationary bicycles during long-term space missions. The researchers found the mean heart rate of the astronauts was 155 beats per minute with a margin of error of 12 beats per minute at a 90 percent confidence level. Which of the following is the most plausible value for the mean heart rate of all astronauts exercising on stationary bicycles during long-term space missions ?

1) 130 beats per minute

2) 140 beats per minute

3) 160 beats per minute

4) 175 beats per minute

Solution:

**Choice C is correct.**

Since, the mean heart rate of the astronauts was 155 beats per minute with a margin error of 12 beats per minute with a 90% confidence level.

Therefore, the **true mean** will be within the margin of error around the **mean **in thisparticular study.

Therefore true mean will be between (155 – 12) and (155 + 12) i.e. 143 and 167 only.

Only one of the given options fall within this range.

Therefore, the most plausible value for the mean heart rate for all astronauts would be **160 beats per minute**.