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THE VISUAL LEARNING STUDIO
See the idea. Understand the connection.
35 visual explanations across 29 chapters, with topic maps throughout the library.
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SEE IT. CONNECT IT. EXPLAIN IT.
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Basic Numeracy — lesson overview
Meaning and conversion
A percentage is a fraction out of one hundred: x% = x/100. To find p% of a quantity, multiply that quantity by p/100.
Useful conversions: 1/2 = 50%; 1/4 = 25%; 1/5 = 20%; 1/8 = 12.5%; 3/4 = 75%. These are identities, not estimation rules.
An increase or decrease is measured relative to its stated base. Percentage change = change ÷ original value × 100.
Different bases produce different percentages
If a price rises from ₹80 to ₹100, the increase is ₹20 on a base of ₹80: 25%. If it then falls from ₹100 to ₹80, the decrease is 20% of ₹100.
The absolute change is the same ₹20, but the denominator differs. Therefore a rise and its reversal need not have the same percentage.
Percentage points compare percentage figures directly. Moving from 20% to 25% is an increase of five percentage points and a relative increase of 25%.
Successive changes: worked example
A 20% rise multiplies a value by 1.20. A 10% fall multiplies the new value by 0.90. Combined multiplier = 1.20 × 0.90 = 1.08.
Starting from ₹100, the final value is ₹108: an 8% net rise, not 10%. The second percentage applies to the changed base.
For signed changes a% and b%, net percentage change = a + b + ab/100. Use a negative sign for decreases.
