For the bolts, any lengths that are more than 4 standard deviations away from the mean (15 cm) will be destroyed. This means that any bolts shorter than 14.6 cm or longer than 15.4 cm will be destroyed.
Percentiles represent the position of a particular measurement within a distribution. For example:
(a) The 15th percentile of head circumference for males 3 to 5 months of age means that 15% of males in that age range have a head circumference of 41.0 cm or smaller.
(b) The 95th percentile of waist circumference for females 2 years of age means that 95% of females in that age group have a waist circumference of 52.7 cm or smaller.
Based on the percentile measurements of standing height for males aged 20 years or older in different age groups, we can conclude that average height tends to decrease with increasing age.