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Let's go through some example computations to find percentages of numbers faster using the tips mentioned earlier:
Example 1: Find 20% of 250 Using the conversion to decimals, 20% becomes 0.20. Now, multiply 250 by 0.20: 20% of 250 = 0.20 * 250 = 50
Example 2: Find 30% of 180 Break down 30% into 10% + 10% + 10%. Then, find 10% of 180 and multiply by 3: 10% of 180 = 0.10 * 180 = 18 30% of 180 = 18 * 3 = 54
Example 3: Find 15% of 360 Use the multiplication shortcut for 10% (0.10) and adjust accordingly: 10% of 360 = 0.10 * 360 = 36 5% of 360 = 0.05 * 360 = 18 15% of 360 = 36 + 18 = 54
Example 4: Find 75% of 80 Since 75% is three-quarters (3/4) of the number, you can find 75% by multiplying by 0.75: 75% of 80 = 0.75 * 80 = 60
Example 5: Find 5% of 400 Use the multiplication shortcut for 5% (0.05): 5% of 400 = 0.05 * 400 = 20
Example 6: Find 35% of 120 Break down 35% into 30% + 5%. Then, find the individual percentages and add them up: 30% of 120 = 0.30 * 120 = 36 5% of 120 = 0.05 * 120 = 6 35% of 120 = 36 + 6 = 42
Example 7: Find a 20% increase of 150 To find a 20% increase, add 20% of 150 to the original number: 20% of 150 = 0.20 * 150 = 30 20% increase of 150 = 150 + 30 = 180
Example 8: Find a 15% decrease of 200 To find a 15% decrease, subtract 15% of 200 from the original number: 15% of 200 = 0.15 * 200 = 30 15% decrease of 200 = 200 - 30 = 170
By practicing these mental math techniques, you can quickly find percentages of numbers without relying on a calculator. With time and familiarity, you'll become even faster and more accurate in your calculations.
