(2.3) Reduction of the standard error In a magnetometry experiment, after a minute of collecting data the statistical noise was reduced to 1 picotesla. For how much longer should data be collected in order to reduce the random error by a factor of 10?

(2.9) Superfluous precision A car covers a distance of 250 m in 13 s; the average speed is calculated to the 10 decimal places of the calculator as 19.230 769 23 m s−1. Explain why it is incorrect to believe all of the significant figures of the quoted speed