The percentage of data values that must be within one, two, and three standard deviations of the mean for data having a bell-shaped distribution can be determined using a. The empirical rule. b. A five-number summary. c. Percentiles. d. Chebyshev's theorem.

a. The empirical rule.

Step-by-step explanation:

The Empirical Rule states that, for a normally distributed(bell-shaped) random variable:

68% of the measures are within 1 standard deviation of the mean.

95% of the measures are within 2 standard deviation of the mean.

99.7% of the measures are within 3 standard deviations of the mean.

So the correct answer is:

a. The empirical rule.

hiking down a winding trail.

step-by-step explanation:

answer: the angel abc is 30°,and the abc is a triangle where the angel bac is 90°

so ac is the half of 24=12ft,and from the pythagorean theorem we find ba

ba=√bc^2-ac^2=√576-144=√432=12√3ft

so bac is 12+12√3=12(1+√3)ft