Question

There are 150 marigold plants in a back yard. Each month, the number of marigold plants decreases by 15%. There are 125 sunflower plants in the back yard. Each month, 8 sunflower plants are removed.
Part A: Write functions to represent the number of marigold plants and the number of sunflower plants in the back yard throughout the months. (4 points)

Part B: How many marigold plants are in the back yard after 3 months? How many sunflower plants are in the back yard after the same number of months? (2 points)

Part C: After approximately how many months is the number of marigold plants and the number of sunflower plants the same? Justify your answer mathematically. (4 points)

Answer 1

Part A-For marigold plants X, a geometric sequence has a general form of:

X = Xo * (1 + r)^n

where r = -15% = -0.15   (negative since it is decreasing)

Xo = the initial amount of marigold plants = 150

X = 150 * (1 – 0.15)^n

X = 150 (0.85)^n