Amount of paper discarded by householdsper week is normally distrubuted with mean .

Standard deviation .

Find the percentage of households throw out at least of paper a week.

Probability density function is given by

,

where is mean for this function and is standard deviation.

Substitute and in the above function.

Probability that household throws out at least of paper a week is .

Using calculator, the value of is .

.

Therefore of the households throw out at least of paper a week.

of the households throw out at least of paper a week.