| A person ordered 5 pairs of black socks and some pairs of brown socks. The price of a black pair was thrice that of a brown pair. While preparing the bill, the bill clerk interchanged the number of black and brown pairs by mistake which increased the bill by 100%. What was the number of pairs of brown socks in the original order? |
A) 10
B) 15
C) 20
D) 25
Correct Answer: D
Solution :
| Let he bought x pairs of brown socks and price of each brown pair = Rs. y |
| Total cost \[=5\times 3y+xy\] |
| Changed cost \[=5\times y+x\times 3y\] |
| According to the question, |
| \[\Rightarrow \] \[\frac{5y+3xy-(15y+xy)}{15y+xy}\times 100=100%\] |
| \[\Rightarrow \] \[5y+3xy=15y+xy+15y+xy\] |
| \[\Rightarrow \] \[5y+3xy=30y+2xy\] |
| \[\Rightarrow \] \[xy=25\,\,\,y\,\,\Rightarrow \,\,x=25\] |
| Hence, original pair of black socks is 25. |
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