Multiple choice

A program consists of two modules executed sequentially. Let $f_1(t)$ and $f_2(t)$ respectively denote the probability density functions of time taken to execute the two modules. The probability density function of the overall time taken to execute the program is given by

  1. $f_1(t)+f_2(t)$
  2. $\int_0^t f_1(x)f_2(x)dx$
  3. $\int_0^t f_1(x)f_2(t-x)dx$
  4. $\max\{f_1(t),f_2(t)\}$
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C Correct answer
Explanation

Probability density function of f1 (t) and f2 (t) is = $\int_0^t f_1(x)f_2(t-x)$