The midday temperature at a hill station on five days was 4°C, -2°C, 0°C, 6°C and -3°C. What was the average midday temperature over those five days?

Add the readings with their signs: 4 - 2 + 0 + 6 - 3 = 5, and 5/5 = 1°C. 3°C adds the sizes only and ignores the minus signs, giving 15/5; below-zero readings pull the total down, they do not push it up. 1.25°C divides the correct total of 5 by 4, leaving the 0°C day out of the count - a day at zero still counts as a day. 2°C throws away the two below-zero days as though they were missing readings, giving 10/5.