BITSAT 2020 Paper

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.