Help Please.

Problem 1: A test is performed on 100 units from the same production as follows: all the units are operated simultaneously, and an inspection is performed every hour when the number of failure units is counted. For simplicity, it will be assumed that the failures occurred "right before the inspection". 1. What is the MTTF (point estimate) value if, after one (1) hour of testing of all the above units, six (6) units fail? 2. What is the MTTF (point estimate) value if all the units failed at #1 are replaced after 1h, and the test is continued and, at the end of the second hour, one more fails, at the end of the 3rd hour two fail, and at the end of 10h three more units are found failed? It is considered that the units failed after the first hour are not replaced. 3. What is the MTTF (point estimate) value for case #2 if all the failed units are immediately replaced when failed? Problem 2: Ten (10) pumps are tested for 1,000 clock hours (calendar hours, each pump is supposed to be tested for this time). During the test, two pumps failed at 400h, and are removed from the test, a third malfunction is observed at 350h but is kept in the test. A failure analysis shows that this is a reliability failure. A fourth pump fails at 350h and is replaced by a new one. A fifth pump malfunctions at 250h, the malfunction is corrected, and the pump is immediately put back to test. 1. What is the MTTF (point estimate) value? 2. Wat is the failure rate of these pumps (calculated in fr/10^6h)