Answer:
option (d) 16.6 and 21.4
Step-by-step explanation:
Data provided in the question:
The mean life for a particular use before they failed = 19.0 hours
The distribution of the lives approximated a normal distribution
The standard deviation of the distribution = 1.2 hours
To find:
The values between which 95.44 percent of the batteries failed
Now,
In Normal distribution, the approximately 95% ( ≈ 95.44% of all values ) falls within 2 standard deviations of the mean
Therefore,
Upper limit = Mean + 2 × standard deviation
⇒ Upper limit = 19.0 + 2 × 1.2 = 21.4
Lower limit = Mean - 2 × standard deviation
⇒ Lower limit = 19 - 2 × 1.2 = 16.6
Hence,
the answer is option (d) 16.6 and 21.4
