Surface Area of Hollowed Hemisphere - Basic Geometry

[anniecvc]

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∏r², so half the sphere is 2∏r².
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∏(1.25²+.93²) = apprx. 15.25 cm².

However, the back of the book says the correct answer is apprx 17.44 cm². So what am I doing wrong?

 

[tiny-tim]

hi anniecvc!

erm …

what about the ring on the top? ​

 

[anniecvc]

thank you tiny tim! i included it before it and the numbers didn't work out, but now it does, so i must've made a simple calculation error. thanks again.