A man ordered 4 pairs of black socks and some pairs of brown socks. The price of a black socks is double that of a brown pair. While preparing the bill the clerk interchanged the number of black and brown pairs by mistake which increased the bill by 50%. The ratio of the number of black and brown pairs of socks in the original order was :

2 : 1

1 : 4

1 : 2

4 : 1

Answer : Option B

Explanation :

Number of brown socks = x

Price of brown socks = Rs. y per pair

Price of black socks = Rs. 2y per pair

$\therefore 4 y+x \times 2 y=\frac{150}{100}(4 \times 2 y+x y)$

$\Rightarrow 4+2 x=\frac{3}{2}(8+x)$

$\Rightarrow 8+4 x=24+3 x$

$\Rightarrow x=24-8=16$

∴ Required ratio = 4 : 16 = 1 : 4

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