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Which of the following is the correct measurement?
26 cm
28 cm
13 cm
14 cm
26 cm
Convert mixed fraction to improper fraction first. Substitute π=722 into the surface area formula 4πr2 to find radius r, then double it to get the diameter.
Surface area of sphere = 2124 \frac{4}{7}$$\text{ cm}^2 =$$\frac{14875}{7}$$\text{ cm}^2, \pi =$$\frac{22}{7}
S=4πr2
Convert mixed fraction to improper fraction first. Substitute π=722 into the surface area formula 4πr2 to find radius r, then double it to get the diameter.
Students often forget to multiply the radius by 2 at the end to find the diameter, or make calculation errors when converting the mixed fraction.
Convert Mixed Fraction to Improper Fraction
Convert the given surface area from a mixed fraction into an improper fraction: 212474=72124×7+4=714868+4=714875 cm2.
S=714875 cm2
Equate Surface Area to Formula
The surface area of a sphere is given by S=4πr2. Substitute S=714875 and π=722.
4×722×r2=714875
Solve for Radius (r)
Simplify the equation to find r2: 788r2=714875⟹88r2=14875⟹r2=8814875=...1352.27... wait, let’s divide properly: 14875/88=169... Let's re-verify: 169×88=14872? Let's check 14875/88: wait, 212474=714872+4=714876. Ah, 2124×7=14868, plus 4=14872. Wait, the question says 212474, let's check 2124×7=14868, plus 4=14872/7. Then 4×722×r2=714872⟹788r2=714872⟹88r2=14872⟹r2=8814872=169. Thus r=169=13 cm.
r2=169⟹r=13 cm
Calculate Diameter (d)
The diameter of the sphere is twice the radius: d=2r=2×13 cm=28 cm. Wait, 2×13=26 cm?! Let's re-multiply: radius r=13, diameter =2×13=26 cm. Wait, let's check option D: 14\text$