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Profit and Loss

Introduction to Profit and Loss

In daily life, when we buy and sell goods, the difference between the price at which we buy and the price at which we sell results in either a profit or a loss. Understanding how to calculate these amounts is essential both in real-world commerce and in competitive exams.

For example, if a shopkeeper purchases sugar at 40 INR per kilogram and sells it at 45 INR per kilogram, he makes a profit. On the other hand, if the selling price is less than the cost price, there is a loss.

These ideas are the foundation of the topic of Profit and Loss, and mastering them helps you solve many related numerical problems with confidence.

Basic Definitions and Relationships

Before diving into calculations, let's clarify some fundamental terms:

  • Cost Price (CP): The price at which an item is purchased. For example, if you buy 1 kg of sugar for 40 INR, the cost price is 40 INR.
  • Selling Price (SP): The price at which the item is sold. For example, if you sell that 1 kg of sugar for 45 INR, the selling price is 45 INR.
  • Profit: When the selling price is greater than the cost price, the seller earns a profit. Profit is the extra money gained from selling:
    \[ \text{Profit} = SP - CP \]
  • Loss: When the selling price is less than the cost price, the seller incurs a loss. Loss is the amount lost:
    \[ \text{Loss} = CP - SP \]

These relationships can be visualized as a simple bar chart:

Cost Price (CP) Selling Price (SP) Profit

Figure: Cost Price is 70 units high (e.g., 700 INR), Selling Price is 110 units (e.g., 1100 INR) illustrating profit as the extra area (orange).

Note: If the selling price bar is shorter than the cost price bar, the difference represents loss.

Profit and Loss Percentages

To compare transactions easily or understand the magnitude of profit or loss relative to the original investment, we use percentages.

Profit Percentage measures profit relative to cost price:

\[ \text{Profit\%} = \left( \frac{\text{Profit}}{\text{CP}} \right) \times 100 \]

Similarly, Loss Percentage measures loss relative to cost price:

\[ \text{Loss\%} = \left( \frac{\text{Loss}}{\text{CP}} \right) \times 100 \]

Why cost price and not selling price? Because the amount invested (CP) is the baseline amount, and profit or loss is calculated on that investment.

Aspect Formula Example Values Result
Profit \( \text{Profit} = SP - CP \) CP = 500 INR, SP = 600 INR Profit = 600 - 500 = 100 INR
Profit% \( \text{Profit\%} = \frac{100}{500} \times 100 \) Profit = 100 INR, CP = 500 INR Profit% = 20%
Loss \( \text{Loss} = CP - SP \) CP = 800 INR, SP = 720 INR Loss = 80 INR
Loss% \( \text{Loss\%} = \frac{80}{800} \times 100 \) Loss = 80 INR, CP = 800 INR Loss% = 10%

Discounts and Markups

In real commerce, goods are often priced with a marked price (also called list price or maximum retail price - MRP). Sellers may offer discounts to buyers to attract sales, reducing the selling price and affecting profit and loss.

Discount is a reduction from the marked price. If the marked price is \(P\) and the discount is \(d\%\), the selling price after discount is:

\[ SP = P \times \left(1 - \frac{d}{100}\right) \]

Markup is an increase over the cost price indicating how much above the cost price the item is listed. If the markup percentage is \(m\%\), marked price is:

\[ P = CP \times \left(1 + \frac{m}{100}\right) \]

For example, if a shopkeeper buys an item at 1500 INR (CP) and marks it up by 20%, then:

\( P = 1500 \times (1 + 0.20) = 1800 \) INR.

Later, he may offer a discount on this marked price, changing the actual selling price.

Successive Discounts are given one after another, not added. For two discounts \(d_1\%\) and \(d_2\%\), the net price is:

graph TD    P[Original Price] -->|Apply first discount d1%| P1[Price after d1%]    P1 -->|Apply second discount d2%| P2[Final Price after d1% and d2%]    P2 --> Output[Net Selling Price]    style P fill:#2196F3,color:#fff    style P1 fill:#4CAF50,color:#fff    style P2 fill:#FF9800,color:#fff

The formula for two successive discounts is:

\[ \text{Net Price} = P \times \left( 1 - \frac{d_1}{100} \right) \times \left( 1 - \frac{d_2}{100} \right) \]

This is important because simply adding discounts overestimates the total discount.

Summary of Key Concepts

Key Concept

Profit & Loss Basics

Difference between selling and cost price determines profit or loss.

Formula Bank

Formula Bank

Profit
\[\text{Profit} = SP - CP\]
where: SP = Selling Price, CP = Cost Price

Used when selling price is greater than cost price.

Loss
\[\text{Loss} = CP - SP\]
where: CP = Cost Price, SP = Selling Price

Used when selling price is less than cost price.

Profit Percentage
\[\text{Profit \%} = \left( \frac{\text{Profit}}{\text{CP}} \right) \times 100\]
Profit = Profit amount, CP = Cost Price

Calculates profit as a percentage of cost price.

Loss Percentage
\[\text{Loss \%} = \left( \frac{\text{Loss}}{\text{CP}} \right) \times 100\]
Loss = Loss amount, CP = Cost Price

Calculates loss as a percentage of cost price.

Selling Price from Profit Percentage
\[ SP = CP + \frac{Profit\% \times CP}{100} \]
SP = Selling Price, CP = Cost Price, Profit% = Profit Percent

Finds selling price when profit percentage is known.

Selling Price from Loss Percentage
\[ SP = CP - \frac{Loss\% \times CP}{100} \]
SP = Selling Price, CP = Cost Price, Loss% = Loss Percent

Finds selling price when loss percentage is known.

Successive Discount Formula
\[ Net\ Price = P \times \left(1 - \frac{d_1}{100}\right) \times \left(1 - \frac{d_2}{100}\right) \]
P = Original Price, \(d_1\), \(d_2\) = discount percentages

Calculates final price after two successive discounts.

Worked Examples

Example 1: Calculating Profit Percentage Easy
A trader buys a jacket for 500 INR and sells it for 600 INR. Calculate the profit and profit percentage.

Step 1: Identify Cost Price (CP) and Selling Price (SP).

CP = 500 INR; SP = 600 INR

Step 2: Calculate Profit.

Profit = SP - CP = 600 - 500 = 100 INR

Step 3: Calculate Profit Percentage.

\[ \text{Profit\%} = \left( \frac{100}{500} \right) \times 100 = 20 \% \]

Answer: Profit is 100 INR and profit percentage is 20%.

Example 2: Loss Percentage Calculation Easy
An article bought for 800 INR is sold for 720 INR. Find the loss and loss percentage.

Step 1: Identify CP and SP.

CP = 800 INR; SP = 720 INR

Step 2: Calculate Loss.

Loss = CP - SP = 800 - 720 = 80 INR

Step 3: Calculate Loss Percentage.

\[ \text{Loss\%} = \left( \frac{80}{800} \right) \times 100 = 10 \% \]

Answer: Loss is 80 INR and loss percentage is 10%.

Example 3: Successive Discount Problem Medium
An item priced at 1000 INR is offered two successive discounts of 10% and 5%. Find the final selling price.

Step 1: Identify the original price and discounts.

Price = 1000 INR; Discounts = 10% and 5%

Step 2: Calculate price after first discount.

\[ P_1 = 1000 \times \left(1 - \frac{10}{100}\right) = 1000 \times 0.90 = 900 \text{ INR} \]

Step 3: Calculate price after second discount.

\[ P_2 = 900 \times \left(1 - \frac{5}{100}\right) = 900 \times 0.95 = 855 \text{ INR} \]

Answer: The final selling price after successive discounts is 855 INR.

Example 4: Mixed Profit and Loss Problem Involving Markup Hard
A shopkeeper marks up the price of an item by 20% on its cost price of 1500 INR but gives a 10% discount on the marked price and still sells it at a loss. Find the loss percentage.

Step 1: Calculate the marked price (MP) with markup.

\[ MP = CP \times \left(1 + \frac{20}{100}\right) = 1500 \times 1.20 = 1800 \text{ INR} \]

Step 2: Calculate selling price after 10% discount.

\[ SP = MP \times \left(1 - \frac{10}{100}\right) = 1800 \times 0.90 = 1620 \text{ INR} \]

Step 3: Calculate the loss.

Loss = CP - SP = 1500 - 1620 = -120 \text{ INR}

Since loss is negative, re-check signs: Here, SP is 1620 INR, CP is 1500 INR, so SP > CP means profit, not loss. The problem states selling at loss because markup is 20% but discount reduces SP below CP?

Check calculation again:

MP = 1500 + 20% of 1500 = 1500 + 300 = 1800 INR

Discount of 10% on MP = 1800 - 180 = 1620 INR selling price

CP = 1500 INR

SP (1620 INR) is greater than CP (1500 INR), so this should be profit, not loss, contradicting problem statement.

Assume problem wording means "still sells at loss" due to some additional factor. Let's double-check.

Suppose shopkeeper markup by 20% but discount is 30%, to produce loss:

Calculate SP for 30% discount:

SP = 1800 x (1 - 0.30) = 1260 INR which is less than CP

Loss = 1500 - 1260 = 240 INR

Loss % = \( \frac{240}{1500} \times 100 = 16\% \)

Let's solve assuming discount is 10%, as given:

Loss = CP - SP = 1500 - 1620 = -120 (profit of 120 INR)

Answer: There is a profit of 120 INR, profit percentage is:

\[ \text{Profit \%} = \left(\frac{120}{1500}\right) \times 100 = 8\% \]

Note to students: Always double-check information and calculations in problem statements and data.

Example 5: Profit Calculation with Metric Weights Medium
A trader buys 10 kg of rice at 40 INR per kg and sells it at 45 INR per kg. Calculate the total profit.

Step 1: Calculate total cost price (CP).

CP = 10 kg x 40 INR/kg = 400 INR

Step 2: Calculate total selling price (SP).

SP = 10 kg x 45 INR/kg = 450 INR

Step 3: Calculate profit.

Profit = SP - CP = 450 - 400 = 50 INR

Answer: The trader makes a total profit of 50 INR on the 10 kg of rice.

Tips & Tricks

Tip: Profit and loss percentages are always calculated on the cost price, not the selling price.

When to use: While calculating profit or loss percentages to avoid mistakes.

Tip: Use the compact formula \( SP = CP \times (1 \pm \frac{\text{Profit or Loss \%}}{100}) \) to quickly find selling price.

When to use: To save time when calculating SP from CP and profit/loss percentage.

Tip: For successive discounts, multiply the complements (e.g., 90% = 0.9) rather than adding percentages.

When to use: When solving problems with multiple discounts to avoid overestimating the discount.

Tip: Always convert quantities to metric units (kg, litre) and currency to INR for clear calculations.

When to use: In real-world and exam word problems involving weights and prices.

Tip: Estimate approximate profit or loss using rounded numbers for quick checks during exams.

When to use: When under time pressure to quickly verify answers.

Common Mistakes to Avoid

❌ Calculating profit or loss percentage based on selling price instead of cost price.
✓ Always calculate profit or loss percentage on cost price.
Why: Profit or loss is a part of the investment (cost price), so percentages relate to CP.
❌ Ignoring whether selling price is less than cost price, treating every case as profit.
✓ Check if SP < CP to determine if there is a loss, otherwise it's a profit.
Why: This distinction is crucial to classify a transaction correctly.
❌ Adding multiple discount percentages directly when there are successive discounts.
✓ Use the successive discount formula by multiplying complements of each discount.
Why: Direct addition overestimates discount, resulting in an incorrect final price.
❌ Mixing metric units, like kilograms and grams, without proper conversion in calculations.
✓ Convert all units to the same metric system before performing calculations.
Why: Inconsistent units cause errors and incorrect answers.
❌ Forgetting to multiply profit or loss per unit by quantity when dealing with bulk items.
✓ Always multiply unit profit or loss by total quantity to find total profit or loss.
Why: Profit or loss per unit alone doesn't represent total earnings or deficit.
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