A wrist watch is sold for Rs.1,200 at a profit per cent equal to its cost price. Find the cost
price of the wrist watch.

Let the cost price (CP) of the wrist watch be Rs. x.
Given, selling price (SP) of the wrist watch = Rs. 1200.
Profit per cent = CP = x.
Therefore, SP = CP + Profit
i. e., SP = x + x% of x
i. e., 1200 = x + (x/100) * x
i. e., x = 300
Hence, the cost price of the wrist watch is Rs. 300.

SP/CP = CP*((100+CP)%) +CP /CP
when SP=1200, above relation only satisfies when CP is kept 300.

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