ABC company follows a certain procedure that requires two tasks to be completed independently in order for a job to be done. On any given day, there is a 7/8 probability that task 1 will be completed on time, and a 3/5 probability that task 2 will be completed on time. On a certain day, what is the probability that task 1 will be completed on time, but task 2 will not?

Since both tasks are independent, therefore the sum of the probability of completion of task 1 + probability of not completing of task 1 = 1

The probability that task 1 will be completed on time is 7/8, and the probability that it will not be completed on time is $$1-\dfrac{7}{8}$$, i.e. $$\dfrac{1}{8}$$

Also, the probability that task 2 will be completed on time is 3/5, and the probability that task 2 will not be completed on time is $$1-\dfrac{3}{5}$$, i.e. $$\dfrac{2}{5}$$

To find the probability that task 1 will be completed on time but task 2 will not, we can multiply these probabilities together:

Probability = (Probability of task 1 being completed on time) * (Probability of task 2 not being completed on time)

Probability = $$\left(\dfrac{7}{8}\right)\left(\dfrac{2}{5}\right)=\dfrac{7}{20}$$

Therefore, the probability that task 1 will be completed on time, but task 2 will not, is $$\dfrac{7}{20}$$

The answer is option D.