Answer:

Explanation:
We are asked to find how much of a 40 gram sample remains after 12 years.
Iron-55 has a half-life of 3 years. Therefore, after 12 years, 4 half-lives have been completed.
- 12 years/3 years = 4 half-lives
Every time a half-life is completed, half of the sample's mass decays. Remember we start with a 40 gram sample.
- 1 half- life: 40 g / 2 = 20 g
- 2 half-lives: 20 g / 2= 10 g
- 3 half-lives: 10 g / 2 = 5 g
- 4 half-lives: 5 g / 2 = 2.5 g
There is also a formula that can be used to solve this problem.

Where A₀ is the initial amount, t is the time, and hl is the half-life.
We know 40 grams is the inital amount, 12 years is the time, and 3 years is the halflife.




After 12 years, <u>2.5 grams </u> of Iron-55 will remain.
Both humans and monkeys have this. A VERY long time ago Humans had very small "strings" of skin. This skin has evolved over time and now there is a bone left. Monkeys are technically un-evolved humans. Good thing they stuck around.
The answer is; B and D
Tapeworms (Cestoda) are called flatworm (Platyhelminthes) while hookworms are roundworms (Nematodes). Both are parasites and live within the intestines of animals and feed on the nutrients digested in the organ. When these worms migrate to other parts of the body, they cause complications, The more of this parasite one has the heavier the symptoms they will exhibit – such as asthma-like symptoms.
Answer:
Calcium is a chemical element with the symbol Ca and atomic number 20.
Explanation: