Q27 / 118 · NTA Abhyas (JEE Main) 2020 · Mathematics · Sequences and Series

The arithmetic mean of two positive numbers a and b exceeds their geometric mean by 32 and the geometric mean exceeds their harmonic mean by 65. If a+b=α and a-b=β, then the value of 10βα is equal to

Correct answer: 6

Solution

A-G=32 and G-H=65
Also, we know that G2=AH
⇒G2=32+GG-65
⇒G2=G2-65G+32G-95
⇒32-65G=95⇒G=95×103=6
G=6⇒A=152
⇒a+b2=152 and ab=6
⇒a+b=15 and ab=36
a-b=a+b2-4ab=225-4×36=9
α=a+b=15, β=a-b=9
⇒10βα=10×915=6

Hence, the correct answer is 6.

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