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1. $(\frac{1}{1.4} + \frac{1}{4.7} + \frac{1}{7.10} + \frac{1}{10.13} + \frac{1}{13.16})$ is equal to = ?

A. $\frac{1}{3}$

B. $\frac{5}{16}$

C. $\frac{3}{8}$

D. $\frac{41}{7280}$

Solution:

(\frac{1}{1.4} + \frac{1}{4.7} + \frac{1}{7.10} + \frac{1}{10.13} + \frac{1}{13.16})

Formula :

\frac{1}{Difference denominator value} \times

[\frac{1}{First value} - \frac{1}{Last value}]

= \frac{1}{3} \times

[1 - \frac{1}{4} + \frac{1}{4} - \frac{1}{7} + \frac{1}{7} - \frac{1}{10} + \frac{1}{10} - \frac{1}{13} + \frac{1}{13} - \frac{1}{16}]

\begin{aligned} = \frac{1}{3} \times [1 - \frac{1}{16}] \\ = \frac{1}{3} \times \frac{15}{16} \\ = \frac{5}{16} \end{aligned}

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