# A machine in a factory has an error rate of 6 parts per 100. The machine normally runs 24 hours a day and produces 90 parts per hour. Yesterday the machine was shut down for 8 hours for maintenance.How many error-free parts did it produce yesterday?

1353.6

Explanation

The hourly error rate for this machine is the error rate in parts per 100 multiplied by the number of parts produced per hour:
$$(\frac{6}{100}) \times 90=0.06 \times 90=5.4 \text { errors per hour }$$
So, in an average hour, the machine will produce 90 - 5.4 = 84.6 error free parts. The machine ran for 24 - 8 = 16 hours yesterday so you would expect that $$16 \times 84.6 = 1353.6$$ error free parts were produced yesterday.