Difference between Datum and Datum feature is<em> 'Datum is theoretical and Datum feature is real'.
</em>
Option: (b)
<u>Explanation:</u>
A Datum is a perfect plane, line, point or surface but only occurs theoretically.
However a Datum Feature is fully based on a tangible surface, axis or point on a part where that theoretical datum is located.
The reason behind in this is they are not equal to each other because the 'part surface' is never 100% perfect.
The important functional features of the Datum is controlled during measurements.
BRIGHT HEADLIGHTS
AND SEVERE WEATHER CONDITIONS
We need to define the variables,
So,

Therefore, the probability that the repair time is more than 4 horus can be calculate as,

The probability that the repair time is more than 4 hours is 0.136
b) The probability that repair time is at least 12 hours given that the repair time is more than 7 hoirs is calculated as,


The probability that repair time is at least 12 hours given that the repair time is more than 7 hours is 0.63