<h3>
Answer: 542.5</h3>
This is equivalent to the fraction 1085/2
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Explanation:
AP stands for "arithmetic progression", which is another name for "arithmetic sequence"
a1 = -10 is the first term
the 15th term happens when n = 15, so
an = a1 + d*(n-1)
a15 = -10 + d(15-1)
a15 = 14d-10
Set this equal to 11 (the stated 15th term) and solve for d
a15 = 11
14d-10 = 11
14d = 11+10
14d = 21
d = 21/14
d = 3/2
d = 1.5 is the common difference
Let's find the nth term
an = a1 + d(n-1)
an = -10 + 1.5(n-1)
an = -10 + 1.5n - 1.5
an = 1.5n - 11.5
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The last term is 41, so we'll replace the 'an' with that and solve for n
an = 1.5n - 11.5
41 = 1.5n - 11.5
41+11.5 = 1.5n
52.5 = 1.5n
1.5n = 52.5
n = (52.5)/(1.5)
n = 35
So the 35th term is 41.
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We're summing n = 35 terms from a1 = -10 to an = 41
S = sum of the first n terms of arithmetic progression
S = (n/2)*(a1 + an)
S = (35/2)*(-10+41)
S = 542.5
The 35 terms add up to 542.5 which is the final answer
As an improper fraction, this converts to 1085/2
