How do I calculate 10% of a number?

Multiply the number by 0.1, or divide by 10. Example: 10% of Rs 5,000 = Rs 500.

How do I calculate percentage increase?

((New - Old) ÷ Old) × 100. Example: price went from Rs 100 to Rs 120: ((120-100)÷100)×100 = 20% increase.

Percentage means "per hundred." The fundamental formula:

Percentage = (Part ÷ Whole) × 100

Example: 45 out of 60 marks = (45 ÷ 60) × 100 = 75%

What is X% of Y?

Answer = (X ÷ 100) × Y

Example: What is 15% of Rs 8,000?

= (15 ÷ 100) × 8,000 = 0.15 × 8,000 = Rs 1,200

This is used for: calculating GST, discounts, tips, commission.

New Value = Original × (1 + Percentage ÷ 100)

Or: Increase Amount = Original × (Percentage ÷ 100)

Example: A salary of Rs 60,000 with a 12% raise:

New salary = 60,000 × (1 + 12/100) = 60,000 × 1.12 = Rs 67,200

New Value = Original × (1 - Percentage ÷ 100)

Example: A product priced Rs 2,000 with 25% discount:

Discounted price = 2,000 × (1 - 25/100) = 2,000 × 0.75 = Rs 1,500

Percentage change = ((New Value - Old Value) ÷ Old Value) × 100

Example: Stock price went from Rs 450 to Rs 522:

Change = ((522 - 450) ÷ 450) × 100 = (72 ÷ 450) × 100 = 16%

If a product costs Rs 1,180 after 18% GST, what is the base price?

Base price = 1,180 ÷ 1.18 = Rs 1,000

Adding 18% GST to a price: Price × 1.18

Removing 18% GST from a GST-inclusive price: Price ÷ 1.18

GST amount only: Price ÷ 118 × 18