John and Smart Sally each need to do their homework. As this is Stats homework, they will need to be able to write, calculate, and read the problems. John likes to write with a pencil but his are too dull and he usually can only find a way to sharpen them 75% of the time. On the other hand 80% of the time at least one pen is working and that will do also. To compute, he can use his cell phone, or a calculator. The chance of the calculator working is 90% and of the cell phone working and being able to do the computation is 70%. To read the problems, he can use a textbook if he remembered to borrow one (he does 80% of the time), or read it on Blackboard (posted 90% of the time).

Smart Sally does her reading, writing, and computing on her computer. It is highly reliable (RComp=.95) but the only way she can read the material is to access it with her computer on the same Blackboard system John uses.

Draw diagrams of the John’s and Sally’ systems

Who has the higher overall probability (reliability) of getting the homework done?