
,

,

We find the probability of intersection using the inclusion/exclusion principle:

By definition of conditional probability,

For

and

to be independent, we must have

in which case we have

, which is true, so

and

are indeed independent.
Or, to establish independence another way, in terms of conditional probability, we must have

which is also true.
The rock hits the gorund at 45s. is the answer
The answer is: "72" .
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(input value, or "x") / 10 = y = f(x);
When y = 7.2, what is the value of "x" ?
x / 10 = 7.2 ;
x = (7.2) * 10 = 72 .
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