RRB NTPC Prelims Model Paper 5 with solutions

(4) 10% water is in the mixture of 100l
So, amount of water
= 10% of 100l
$=\frac{10\times 100\mathit{l}}{100}=10\mathit{l}$
∴p amount of milk = (100 – 10)l= 90 l
Let adding x l water in the mixture, the amount of milk will be 50%.
So, 50% of (100 + x) = 90 l
$\Rightarrow \frac{50\times 100+\mathit{x}}{100}=90\mathit{l}$
$\Rightarrow \left(100+\mathit{x}\right)=\frac{90\mathit{l}\times 100}{50}=180\mathit{l}$
∴x = 180l – 100l = 80l.