If the survivorship at the start of October is 0.4,how many mice died during the month of September?
A) 10
B) 16
C) 30
D) 72
E) 90

Question

Quizplus · Accepted Answer

The survivorship at the start of the month is the number of individuals that survived to the end of the previous month. Therefore, if the survivorship at the start of October is 0.4, then 40% of the population survived from September to October.

Let X be the initial population in September. 
40% of X survived to October. 
Therefore, 60% of X died during September.

We can set up the equation:

0.4X = survivors 
0.6X = dead

We want to solve for the number of mice that died:

0.6X = number of mice that died

We don't know the value of X, but we can see that the answer will be some multiple of 0.6.

To find the best answer choice, we need to look for a multiple of 0.6 among the answer choices.

A: 10 --> not a multiple of 0.6 
B: 16 --> not a multiple of 0.6 
C: 30 --> 0.6 x 50 = 30, so this works 
D: 72 --> not a multiple of 0.6 
E: 90 --> not a multiple of 0.6

Therefore, the answer is C: 30.

If the Survivorship at the Start of October Is 0