Find the fourth proportional of 4a + 7, 11a + 3 and 6a if a = 2.
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Correct answer: B
Explanation
The correct answer is option 2 i.e 20.
(4a + 7) : (11a + 3) = (6a) : x
Substitute a = 2 into the equation
⇒ 4a + 7 = 4(2) + 7 = 8 + 7 = 15
⇒ 11a + 3 = 11(2) + 3 = 22 + 3 = 25
⇒ 6a = 6(2) = 12
So, the equation becomes = 15 : 25 = 12 : x
⇒ 15 × x = 25 × 12
⇒ 15x = 300
⇒ x = 300 ÷ 15 = 20