The Student Room Group
Reply 1
C4>O7
From 2000 SMC:

16. A roll of adhesive tape is wound round a central cylindrical core of radius 3cm. The outer radius of a roll containing 20m or tape is 4cm. Approximately what is the outer radius of a roll containing 80m of tape?

A 5cm B 5.5cm C 6cm D 7cm E 12cm

5.5 right?

The 20m tape is wound round so that the total area of the wound disk is 5pi cm^2. The ratio of 20m to 5pi must be the same for the area of the larger disk and the 80m.
Reply 2
C4>O7
From 2000 SMC:

16. A roll of adhesive tape is wound round a central cylindrical core of radius 3cm. The outer radius of a roll containing 20m or tape is 4cm. Approximately what is the outer radius of a roll containing 80m of tape?

A 5cm B 5.5cm C 6cm D 7cm E 12cm

I got 7...... (But I *usually* trust james so go with him answer!)
Reply 3
Katie Heskins
I got 7...... (But I *usually* trust james so go with him answer!)

I wouldnt trust me on this, i *usually* do appaulling in the SMC :tongue:
Reply 4
JamesF
5.5 right?

The 20m tape is wound round so that the total area of the wound disk is 5pi cm^2. The ratio of 20m to 5pi must be the same for the area of the larger disk and the 80m.


I think the approach is correct, but i get 6 as an answer :frown: :