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The number of students in a school went up from 640 one year to 720 the next. Find the percentage increase.

Class 7Comparing QuantitiesComparing Quantities
  • A80%
  • B11.11%
  • C12.5%
  • D1.25%

Step-by-Step Solution

Increase = 720 − 640 = 80. Percentage increase is always measured against the ORIGINAL value: . 11.11% is — dividing by the new figure instead of the old one. 80% reads the raw rise of 80 students as a percentage, and 1.25% forgets that must still be multiplied by 100.
Answer: C) 12.5%

Key idea: Three forms of the same number

Fractions, decimals, and percentages are three notations for the same idea. Convert freely:

- **Fraction → percentage**: multiply by 100. .
- **Percentage → fraction**: divide by 100 and simplify. .
- **Decimal → percentage**: shift two places right. 0.34 = 34%.
- **Percentage → decimal**: shift two places left. 8% = 0.08.

With practice, this becomes automatic and you can move between forms without thinking.

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