Using the data provided in the reliability block diagram $($RBD$),$

After completing the "series analysis" of the system, you have been asked which component is a candidate for an improvement initiative?

R$1$

R$2\mathrm{.}1,$ R$2\mathrm{.}2,$ R$2\mathrm{.}3$

R$3,$ R$4$

R$5\mathrm{.}1,$ R$5\mathrm{.}2,$ R$5\mathrm{.}3$ & R$5\mathrm{.}4$

R$6$