RRB NTPC Prelims Model Paper 5 with solutions

(1) Total gain % = 10%
∴gain = 10% of 100 kg.
$=100\mathit{k}\mathit{g}\times \frac{10}{100}=10\mathit{k}\mathit{g}.$
Let the part of 7% gain
= x kg. and the part of 17%
gain = (100 – x) kg
∴ By question,
7% of x + 17% of (100 – x)
= 10 kg
$\Rightarrow \frac{7\mathit{x}}{100}+\frac{\left(100-\mathit{x}\right)17}{100}=10$
$\Rightarrow \frac{7\mathit{x}+1700-17\mathit{x}}{100}=10$
⇒ –10x + 1700 = 1000
⇒ –10x = 1000 – 1700 = –700
$\Rightarrow \mathit{x}=\frac{-700}{-10}=70\mathit{k}\mathit{g}.$