Can someone please answer this question below? Thanks! Will give medal.

Question

anonymous · Answer

Link to question: http://imgur.com/nyH4jtN

sepeario · Answer

ok firstly do you know the outer diameter?

anonymous · Answer

Nope it's not written

sepeario · Answer

Okay on the ruler it shows that one side of the circle is from 4cm, and the other side measures 7.4. What is the difference between these two?

anonymous · Answer

3.4 cm

sepeario · Answer

Good! If the wall is 3mm thick or 0.3cm thick, and there is a wall on both sides, that means that it must be times 2, or 0.6cm in total. So what is the inner diameter if you have to subtract the wall from the outer diameter?

anonymous · Answer

2.8 cm?

sepeario · Answer

Yes! Well done.

anonymous · Answer

Wow thanks for your help! I wrote 7.4cm in the exam paper. :/ I didn't have to time to think as the teacher was like "Give, give now!"