Question
What is the sum of this arithmetic series: 7 + 12 + 17 + 22 + … + 72?
A. 525
B. 533
C. 553
D. 500
Answer: C. 553
Solution:
The arithmetic series is 7 + 12 + 17 + 22 + … + 72
12 – 7 = 5
17 – 12 = 5
=> Common difference: d = 5
a1 = 7
an = a1 + (n – 1) * 5
an = 72, n = ?
7 + (n – 1) * 5 = 72
n = 14
s14 = 14 * (a1 + a14) / 2
s14 = 14 * (7 + 72) / 2
s14 = 553
Hence, The sum of the arithmetic series is 7 + 12 + 17 + 22 + … + 72 = 553.
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