A Random Sample of 20 Mixed Gender Twins Is Selected $\overline{d}$

Multiple Choice

A random sample of 20 mixed gender twins is selected and their resting pulse rate is taken after a 5 minute period of relaxing on a sofa. The average resting pulse rate for the male twins was 67 betas per minute and for the female twins it was 73 beats per minute, resulting in $\overline{d}$ = -6 . The standard deviation of the differences in pulse rates between the male and female twins was 3.4 beats per minute. What is the standard error of $\overline{d}$ ?

A) 0.17
B) 0.76
C) 3.4
D) 5