Amy had 30 CDs
The mean playing time of these was 42mins
She sold 5
The mean playing time of the 25 left is now 42.8
Calculate the mean playing time of the 5 CDs that Amy sold.
Method please.
2)She shutter speed S of a camera varies inversely as the square of the aperture setting, F. When F=8, S=125. Is this the same as the proportional formula where F=KS?