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1. If 7 spiders make 7 webs in 7 days, then 1 spider will make 1 web in how many days?

A. 1

B. $\frac{7}{2}$

C. 7

D. 49

Solution:

Let the required number days be x.
Less spiders, More days (Indirect Proportion)
Less webs, Less days (Direct Proportion)

\begin{matrix} Spiders 1 : 7 \\ Webs 7 : 1 \end{matrix}} :: 7 : x

\begin{aligned} ∴ 1 \times 7 \times x = 7 \times 1 \times 7 \\ \Rightarrow x = 7 \end{aligned}

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