We have 3 white balls in the first urn out of 9. That means we have a 1 in 3 chance at picking the white ball in the first urn.
Now, we have a 3 in 11 chance at picking the white ball in the second urn.
Since, we want them simultaneously, we need to multiply them.
1/3 × 3/11 = 1/11 chance
4.05 in a mixed number is 4 1/2
Answer: Choice A
S9 = (9/2)*(2+26)
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The formula is
Sn = (n/2)*(a1+an)
where
Sn = sum of the first n terms (nth partial sum)
n = number of terms
a1 = first term
an = nth term
In this case,
n = 9
a1 = 2 (plug in n = 1 into the formula an = 3n-1 and simplify)
an = a9 = 26 (plug n = 9 into the formula an = 3n-1 and simplify)
So,
Sn = (n/2)*(a1+an)
S9 = (9/2)*(2+26)
will help us find the sum of the first 9 terms of this arithmetic sequence
