Find the indicated sum.
-$$\sum _ { i = 6 } ^ { 9 } \frac { 1 } { i - 1 }$$
A) $- \frac { 259 } { 1296 }$
B) 26
C) $\frac { 107 } { 504 }$
D) $\frac { 533 } { 840 }$

Question

Quizplus · Accepted Answer

The sum can be calculated by substituting the values of $i$ from 6 to 9 into the given formula $\frac{1}{i-1}$ and adding the results: $$\sum _ { i = 6 } ^ { 9 } \frac { 1 } { i - 1 } = \frac{1}{5} + \frac{1}{6} + \frac{1}{7} + \frac{1}{8}$$ To find the sum, find a common denominator and add the fractions: $$\frac{1}{5} + \frac{1}{6} + \frac{1}{7} + \frac{1}{8} = \frac{168 + 140 + 120 + 105}{840} = \frac{533}{840}$$

Find the Indicated Sum ∑i=691i−1\sum _ { i = 6 } ^ { 9 } \frac { 1 } { i - 1 }i=6∑9​i−11​

Find the Indicated Sum $\sum _ { i = 6 } ^ { 9 } \frac { 1 } { i - 1 }$