- #1

anniecvc

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I need to find the total surface area of the hollowed out hemisphere (picture attached), with an inner diameter of 1.86 cm and what looks like an outer radius (also what I am assuming as height) of 1.25 cm.

Surface area of a sphere is 4∏r

Since the outer hemisphere has a radius of 1.25 cm, its SA is 2∏(1.25cm)

2∏(1.25

However, the back of the book says the correct answer is apprx 17.44 cm

Surface area of a sphere is 4∏r

^{2}, so half the sphere is 2∏r^{2}.Since the outer hemisphere has a radius of 1.25 cm, its SA is 2∏(1.25cm)

^{2}. The inner hemisphere has a diameter of 1.86cm, therefore a radius of .93 cm. Inner hemisphere then as a SA of 2∏(.93cm)^{2}. Adding the two SA, I get:2∏(1.25

^{2}+.93^{2}) = apprx. 15.25 cm^{2}.However, the back of the book says the correct answer is apprx 17.44 cm

^{2}. So what am I doing wrong?