Probability that the electronic component fails when first used is P(F)=0.10. Therefore, P(F′)=1−P(F)=0.90 Let E be the event that a new component will last for one year. Then, P(E)=P(F)P(
E
F
)+P(F′)P(
E
F′
) [total probability theorem] =0.10×0+0.90×0.99=0.891.