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If the radius of a hemisphere is increased by 50%, then find the percentage increase in the volume. (Take π=722)
112.5%
150%
125%
137.5%
125%
Use successive percentage change or ratio method: for a 3D volume, scaling factor k=1+50%=1.5. The new volume is V2=V1×(1.5)3=3.375V1. Percentage increase = (3.375−1)×100%=237.5%−100%=125%. Alternatively, successive percentage for volume with 3 dimensions: 50+50+50+⋯=125%.
Radius of hemisphere is increased by 50%
V=32πr3
Use successive percentage change or ratio method: for a 3D volume, scaling factor k=1+50%=1.5. The new volume is V2=V1×(1.5)3=3.375V1. Percentage increase = (3.375−1)×100%=237.5%−100%=125%. Alternatively, successive percentage for volume with 3 dimensions: 50+50+50+⋯=125%.
Many students mistakenly calculate percentage increase using the formula for area (r2) instead of volume (r3), leading to incorrect answers like 125% applied incorrectly or missing the cubing of the scale factor.
Step 1: Write the volume formula for a hemisphere
The volume (V) of a hemisphere in terms of its radius (r) is given by the formula: V=32πr3
V=32πr3
Step 2: Determine the new radius after a 50% increase
If the initial radius is r, an increase of 50% makes the new radius (r′) equal to: r′=r+0.50r=1.5r=23r
r′=1.5r
Step 3: Calculate the new volume (V′)
Substitute the new radius into the volume formula: V′=32π(r′)3=32π(1.5r)3=32π(3.375r3)=3.375V
V′=3.375V
Step 4: Find the percentage increase in volume
The percentage increase is calculated as VV′−V×100%. Substituting V′=3.375V: Percentage Increase=V3.375V−V×100%=2.375×100%=237.5%−100%=125% Wait, 3.375−1=2.375, and 2.375\times 100 = 2$