The Switch is switched off once the temperature falls below 18 and then it is turned on when the
temperature is more than 21. When the temperature is more than 21. Identify the Equivalance values which belong to the same class.
the replies i seen are good and correct,Actually there is no difficulty in the question because you already mentioned that , the ECP for "temperature more than 21", so out of four options "C" has all numbers more than 21
so c is the answer
but if you doesn't mention the temperature like more than 21and if you ask the question like this
1. <18 3% of temp
2.18<= =>21 5% of temp
3.21< 10% of temp
then there will be confusion in which way we need to partition the class.....
Try in this way and enjoy....