As follows:
You can now complete the problem.
(The £ sign in the 6'th line should be a 3 of course!!)
Note that log2(2x)=log2(2)+log2(x) and log2(2)=1
Alternatively, you can do it the long way by noting that the n'th term of the geometric sequence is given by 2n+2.
See https://web2.0calc.com/questions/product_3#r2
Here's one way:
Note that 2a2b2c....=2a+b+c...
In your case a+b+c forms an infinite geometric series, ie. b=ar,c=ar2,...etc
The limit of the infinite geometric series here is a1−r or 1/31−1/3
You can complete the calculation.
As follows, I think:
I think you mean that 18 is the number of degrees of freedom! Look in some chi-square distribution tables (e.g. https://en.wikibooks.org/wiki/Engineering_Tables/Chi-Squared_Distibution) along the row for DF = 18 until you get to a number close to 21.6, then look at the column heading for the probability.
(NB: In the reference above the probabilities represent greater than rather than less than, so you would need to subtract the resulting probability from 1 for your case.)
Try this:
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