Find the Standard Deviation

Question

Scrapie is a degenerative disease of the nervous system. A study of the substance IDX as a treatment for scrapie used as subjects 20 infected hamsters.

Ten, chosen at random, were injected with IDX. The other 10 were untreated. The researchers recorded how long each hamster lived. They reported: 

Thus, although all infected control hamsters had died by 94 days after infection (mean  ± SEM = 87.4 ± 2.02), IDX-treated hamsters lived up to 121 days (mean  ± SEM = 111.8 ±2.72). Readers are supposed to know that SEM stands for the standard error of the mean.

(A) for the group injected with IDX, find:

the mean: X = _____

standard deviation: s = _____

(B) for the untreated group, find:

the mean: X = _____

standard deviation: s = _____

I have found that the mean for part A, is 111.8, and the mean for part B is, 87.4 but I cannot get the SD.

Answer 1

(A) For the group injected with IDX, find:

the mean: X = 111.8

standard deviation: s = 2.72

(B) For the untreated group, find:

the mean: X = 87.4

standard deviation: s = 2.02