1. **Stating the problem:** Understand the concept of Ratio and solve typical ratio problems seen in competitive exams like GMAT or bank job exams. 2. **Concept of Ratio:** A ratio compares two quantities showing how many times one value contains or is contained within the other. It is written as $a:b$ or $\frac{a}{b}$ where $a$ and $b$ are quantities. 3. **Important rules:** - Ratios can be simplified like fractions by dividing both terms by their greatest common divisor (GCD). - Ratios can be scaled up or down by multiplying or dividing both terms by the same number. - If $a:b = c:d$, then $a \times d = b \times c$ (cross multiplication). 4. **Typical problem type:** Given ratios and total quantities, find individual parts. 5. **Example problem:** The ratio of boys to girls in a class is 3:4. If there are 21 boys, how many girls are there? 6. **Solution:** - Let the number of girls be $x$. - Given ratio $\frac{boys}{girls} = \frac{3}{4}$. - Substitute values: $\frac{21}{x} = \frac{3}{4}$. - Cross multiply: $3x = 21 \times 4$. - Simplify: $3x = 84$. - Divide both sides by 3: $x = \frac{84}{3} = 28$. 7. **Answer:** There are 28 girls in the class. This type of problem is common in exams and tests your understanding of ratio concepts and cross multiplication.