The radius of a circle is increased by 50%. What is the percentage increase in t

Practice Questions

Q1
The radius of a circle is increased by 50%. What is the percentage increase in the area of the circle? (2020)
  1. 50%
  2. 75%
  3. 100%
  4. 125%

Questions & Step-by-Step Solutions

The radius of a circle is increased by 50%. What is the percentage increase in the area of the circle? (2020)
  • Step 1: Identify the original radius of the circle, which we will call 'r'.
  • Step 2: Calculate the new radius after a 50% increase. The new radius is 1.5 times the original radius, so it is 1.5r.
  • Step 3: Write the formula for the area of a circle, which is Area = πr².
  • Step 4: Calculate the original area using the original radius: Original Area = πr².
  • Step 5: Calculate the new area using the new radius: New Area = π(1.5r)².
  • Step 6: Simplify the new area: New Area = π(1.5r)² = π(2.25r²) = 2.25πr².
  • Step 7: Find the increase in area by subtracting the original area from the new area: Increase in Area = New Area - Original Area = 2.25πr² - πr².
  • Step 8: Simplify the increase in area: Increase in Area = (2.25 - 1)πr² = 1.25πr².
  • Step 9: Calculate the percentage increase in area: Percentage Increase = (Increase in Area / Original Area) × 100%.
  • Step 10: Substitute the values: Percentage Increase = (1.25πr² / πr²) × 100% = 1.25 × 100% = 125%.
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