A laboratory technician records the life span (in months) of rats treated at birth with a fertility hormone. From the frequency distribution below, find the mean life span. Please round your answer to the nearest tenth.
A) mean life span = 11.4 months
B) mean life span = 10.3 months
C) mean life span = 10.2 months
D) mean life span = 9.7 months
E) mean life span = 8.5 months

Question

A laboratory technician records the life span (in months) of rats treated at birth with a fertility hormone. From the frequency distribution below, find the mean life span. Please round your answer to the nearest tenth. 
A) mean life span = 11.4 months 
B) mean life span = 10.3 months 
C) mean life span = 10.2 months 
D) mean life span = 9.7 months 
E) mean life span = 8.5 months

Quizplus · Accepted Answer

To find the mean lifespan, we need to calculate the sum of all lifespans divided by the total number of rats. We can use the midpoint of each class interval as a representative value for that interval. Thus, the midpoint of the first interval (5-7 months) is 6 months, the midpoint of the second interval (8-10 months) is 9 months, and so on.

To calculate the sum of all lifespans, we multiply each midpoint by its corresponding frequency, and then add up these products.

(6 x 3) + (9 x 14) + (12 x 21) + (15 x 6) = 234

To calculate the total number of rats, we add up all the frequencies:

3 + 14 + 21 + 6 = 44

Finally, we compute the mean by dividing the sum of lifespans by the total number of rats:

234 / 44 = 10.2 months

Therefore, the answer is C.

A Laboratory Technician Records the Life Span (In Months) of Rats