Question 71

x is the $$4^{th}$$ proportional to 12, 16 and 5; and 20, y, 15,21 are in proportion. Then the value of (6x - y) is:

Solution

x is the $$4^{th}$$ proportional to 12, 16 and 5 (given)

so, $$\frac{12}{16}=\frac{5}{x}$

x = $$\frac{20}{3}$$

20, y, 15,21 are in proportion ( given)

so, $$\frac{20}{y}=\frac{15}{21}$$

y = 28

Now,

Required expression : ( 6x - y )

$$\therefore\ \left(\ 6\times\frac{20}{3}\right)-28$$

$$\therefore\ 40-28=12\ $$

Hence, Option D is correct.

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