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Given that p:q = \(\frac{1}{3}\):\(\frac{1}{2}\) and q:r = \...

Given that p:q = \(\frac{1}{3}\):\(\frac{1}{2}\) and q:r = \(\frac{2}{5}\), find p:r

A.

4:105

B.

7:15

C.

20:21

D.

2:35

E.

3:20

Correct answer is B

\(p : q = \frac{1}{3} : \frac{1}{2}\)

\(\frac{p}{q} = \frac{2}{3}\)

\(2q = 3p ... (1)\)

\(q : r = \frac{2}{5} : \frac{4}{7}\)

\(\frac{q}{r} = \frac{2}{5} \times \frac{7}{4} = \frac{7}{10}\)

\(10q = 7r ... (2)\)

Eliminating q, we have

(1) : \(2q = 3p \)

\(10q = 15p\)

\(\implies 15p = 7r\)

\(\therefore \frac{p}{r} = \frac{7}{15}\)

\(p : r = 7 : 15\)