Suresh sold a watch at Rs 105 and earned a profit of 20%. What was his cost price?

Options

A. Rs 87.50
B. Rs 84
C. Rs 90
D. Cannot be determined

Answer

To find Suresh's cost price (CP) of the watch, we can follow these steps:

### Step 1: Identify the Selling Price (SP) and Profit Percentage
- The selling price (SP) of the watch is given as Rs 105.
- The profit percentage is given as 20%.

### Step 2: Use the Profit Percentage Formula
The profit percentage can be calculated using the formula:
\[ \text{Profit Percentage} = \frac{\text{SP} - \text{CP}}{\text{CP}} \times 100 \]
Substituting the known values:
\[ 20 = \frac{105 - \text{CP}}{\text{CP}} \times 100 \]

### Step 3: Rearrange the Equation
To eliminate the percentage, we can rearrange the equation:
\[ 20 = \frac{105 - \text{CP}}{\text{CP}} \times 100 \]
Dividing both sides by 100 gives:
\[ 0.2 = \frac{105 - \text{CP}}{\text{CP}} \]

### Step 4: Cross-Multiply
Cross-multiplying gives:
\[ 0.2 \times \text{CP} = 105 - \text{CP} \]

### Step 5: Combine Like Terms
Rearranging the equation gives:
\[ 0.2 \times \text{CP} + \text{CP} = 105 \]
This simplifies to:
\[ 1.2 \times \text{CP} = 105 \]

### Step 6: Solve for CP
Now, divide both sides by 1.2 to find the cost price:
\[ \text{CP} = \frac{105}{1.2} \]

### Step 7: Calculate the Value
Calculating the division:
\[ \text{CP} = \frac{1050}{12} = 87.5 \]

### Conclusion
Thus, Suresh's cost price (CP) of the watch is Rs 87.5.

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