Software-Reliability

Question 1

The following table shoes the time between failures for a software system



The reliability of the system for one hour of operation assuming an exponential model is

A
0.45
B
0.63
C
0.84
D
0.95
Question 1 Explanation: 
MIBF = ∑(Start of downtime - Start of uptime)/No. of failures
MIBF = (6+4+8+5+6)/5 = 29/5
The probability or reliability that the product will work for a defined period of time without failure is given by
R(T) = exp(-T/MTBF); T = 1 hour
R(1) = e(-1/(29/5)) = e(-5/29) = 0.84
Question 2
The following table shows the time between failures for a software:
Error number 1 2 3 4 5
Time since last failure (hour) 6 4 8 5 6
 
The reliability of the system for one hour operation assuming an exponential model is
A
e -9/29
B
e -7/29
C
e -5/29
D
e -3/29
Question 2 Explanation: 
To calculate the reliability of the system for one hour of operation using an exponential model, you can use the formula: Reliability (R) = e^(-λt) Where: λ (lambda) is the failure rate, which can be calculated as the reciprocal of the mean time between failures (MTBF), and t is the time of interest, which in this case is 1 hour. First, let's calculate λ. The MTBF is the average time between failures, which can be calculated as the sum of the time since the last failure divided by the number of failures. MTBF = (6 + 4 + 8 + 5 + 6) / 5 = 29/5 hours Now, calculate λ: λ = 1 / MTBF = 5 / 29 per hour Now, calculate the reliability for 1 hour of operation: R = e^(-λt) = e^(-(5/29) * 1) = e^(-5/29) So, the reliability of the system for one hour of operation assuming an exponential model is approximately e^(-5/29).
Question 3
Consider a software program that is artificially seeded with 100 faults. While testing this program, 159 faults are detected, out of which 75 faults are from those artificially seeded faults. Assuming that both real and seeded faults are of same nature and have same distribution, the estimated number of undetected real faults is ______.
A
28
B
175
C
56
D
84
Question 3 Explanation: 
Total faults detected = 159
Real faults detected among all detected faults = 159 - 75 = 84
Since probability distribution is same, total number of real faults is (100/75)*84 = 112
Undetected real faults = 112- 84 = 28
There are 3 questions to complete.

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