7.6 Six measurements of the length of a wooden block gave the following measurements: 20.3, 20.4, 19.8, 20.4, 19.9, and 20.7 cm.

(a) Estimate the mean and the standard error of the length of the block;

(b) Assume that the block is known to be of length  D 20 cm. Establish if the measurements are consistent with the known length of the block, at the 90%

probability level.