Answer
2 time intervals
Final amount is 10
Final amount is reasonable
Work Step by Step
$14/7=2$
$40*1/2^2$
$40*1/4$
$10$
The half life of the item in question is 7 years. This means, after 7 years, the quantity of the item is halved. Since we are told 14 years have passed, we divide 14 by 7 to find there have been two half lives.
For an item that has passed one half life, we know the item would have half of its original quantity. For an item that has passed two half lives, we know the item would have $(1/2)^2$, or $1/4$ of its original quantity remaining.
The original quantity of the item was 40 units, and since we know there have been two half lives, we multiply 40 by 1/4 to find 10 units of the item remain.
