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[kpkanupriyakhmi]

Lin and Mark each attempt to decode a msg. If P of Lin solving is 0.80 and for Mark is 0.70 then what is P of at least one of them solving the msg.
My doubt:-
What I did was 1-(0.80)(0.70)
Why is this wrong.
And when we calculate by this method:-
(0.80)(0.70)+(0.80)(0.30)+(0.70)(0.20)
It was correct again why and why were 0.30 and 0.70 included
Please reply ASAP

[tommywallach]

Hey Kp,

.8 * .7 = the odds that BOTH of them solve it.

So 1 - (.8 * .7) = the odds that BOTH of them do not solve it. However, that could be EITHER that one of them does and the other does not, OR that both of them fail. That's not what the question asks for.

The other method is adding up the three possibilities that fit the constraint in the question:

.8 * .7 = both of them solve
.8 * .3 = Lin solves but Mark does not solve
.7 * .2 = Mark solves but Lin does not solve

Add those up, and you get the odds that at least one of them succeeds.

-t