Suppose the functions F and G can be computed in 5 and 3

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Suppose the functions F and G can be computed in 5 and 3 nanoseconds by functional units U_F and U_G, respectively. Given two instances of U_F and two instances of U_G, it is required to implement the computation F(G(X_i)) for 1 ≤ i ≤ 10. Ignoring all other delays, the minimum time required to complete this computation is _______ nanoseconds.

1. 28
2. 13
3. 38
4. 7

Correct Option: A

This concept is used in pipelining. The important thing here is U_F as it takes 5 ns while U_G takes 3 ns only. One have to do 10 such calculations. According to question, we have 2 instances of U_F and U_G respectively. So, U_F can be done in 50 / 2 = 25 nano seconds. For the start, U_F needs to wait for U_G output for 3 ns and rest all are pipelined and hence no more wait. Therefore, the answer will be :
3 + 25 = 28 ns