Question: Two numbers A and B are in the ratio of 4 : 5. Their average is 180. If A is increased by 20% then to get the average increased by 25\displaystyle\frac{5}{9}\%, B will increase by
(a) 40
(b) 50
(c) 60
(d) 70
Ans: (c) 60
Explanation:
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Let, A = 4x, B = 5x
\therefore 4x + 5x = 2 \times 180
\Rightarrow x = 40
Hence, A = 160
\quad & B = 200
New case:
A = 160 \times \displaystyle\frac{120}{100} = 192
B = B’
\begin{aligned}
&\quad \frac{192+\text{B'}}{2}=180\times 125\frac{5}{9}\%\\[1.5em]
&\Rightarrow 192+\text{B'}=360\times \frac{1130}{9\times 100}=452\\[1.5em]
&\Rightarrow \text{B'} = 260
\end{aligned}
Hence, B is increased by 60.
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