Answer:
It seems there's more information in you question that you haven't posted.
7 months = 7 * (365/12) = 213 days
The half-life of chromium 51 is 27.7 days.
After 7 months, chromium 51 will have undergone 7.69 half-lives.
To solve for the ending amount we'll use the formula:
Ending Amount = Beginning Amount / 2^n where 'n' = # of half-lives
We'll say the beginning amount =1
Ending Amount = 1 / 2^7.69
Ending Amount = 0.0048426082
Basicaly if you started with 1 gram of chromium 51, after 7 months you would have 0.0048426082 grams.
Source: https://www.1728.org/halflife.htm
Step-by-step explanation:
