41-48: Half-Life. Each exercise gives a half-life for an exponentially decaying quantity. Answer about the quantity's decay.

This is 41. The half-life of a radioactive substance is 40 years. if you start with some amount of this substance. what fraction of that amount will remain in 80 years? in 120 years?

The answer to 41 is 1/4; 1/8th.

This is number 45. The current population of a threatened animal species is 1 million, but it is declining with a half-life of 24 years. How many animals will be left in 30 years? in 70 years?

The answer to this about 120,000 animals; about 132,000 animals.

49-52: Approximate Half-Life Formula. Use the approximate half-life. Discuss whether the formula is valid for the case described.

This is number 49. Urban encroachment is causing the area of a forest to decline at a rate of 6% per year. What is the appropriate half-life of the forest? Based on this approximate half-life about what fraction of the forest will remain in 50 years?

The answers to 49 are 11.7 years; 0.05.

This is from my Math 140 course at Sacramento City College-online. Understanding Mathematics. A Quantitative Reasoning Approach. 7th Edition. By Bennett Briggs. Course #18374. Please use good grammar, cut long answers to the best of your ability. Watch grammar, spelling, etc.