Explanation
Given, radius r=2.8 cm.
We know that, the surface area of a sphere of radius r =4πr2
=4×227×2.8×2.8
=98.56cm2.
Let radius of sphere be r cm.
We know, surface area of sphere =4πr2
⟹ 221.76cm2=4πr2
⟹ r2=221.764π=221.76×74×22=17.64
⟹ r=√17.64=4.2cm .
Then, diameter of the sphere, d=2r=2×4.2=8.4cm.
Therefore, option A is correct.
The formula for calculating the surface area of a cuboid of dimensions :
l \times b \times h is :
2\times (l\times b+b\times h+h\times l)
Substituting,
l=10cm
b=4cm
h=3cm
Surface area = 2\times (10\times 4+4\times 3+3\times 10)
= 2\times (40 + 12 + 30)
= 2\times 82 { cm }^{ 2 }
= 164 { cm }^{ 2 }
Hence, the answer is option (C)
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