If the A.M and G.M of two numbers are 13 and 12 respectively then the two numbers are
If the A.M and G.M of two numbers are 13 and 12 respectively then the two numbers are
A) 10, 18
B) 12, 18
C) 8, 18
D) 8, 12
2 Answers
Correct option is (C) 8, 18
Let both numbers are a and b.
\(\therefore\) Their arithmetic mean \(=\frac{a+b}2\)
& their geometric mean \(=(ab)^\frac12\)
\(\therefore\) \(\frac{a+b}2=13\)
And \((ab)^\frac12=12\) (Given)
\(\Rightarrow a+b=26\) _______________(1)
& \(ab=12^2=144\) _______________(2)
\(\therefore(a-b)^2=(a+b)^2-4ab\)
\(=(28)^2-4\times144\)
\(=676-576\)
\(=100=10^2\)
\(\Rightarrow a-b=10\) _______________(3)
By adding (1) & (3), we get
\((a+b)+(a-b)=26+10\)
\(\Rightarrow2a=36\)
\(\Rightarrow a=\frac{36}2=18\)
\(\therefore b=26-a\)
\(=26-18=8\) (From (1))
Hence, required numbers are 8 and 18.