So if you have?

Question

okay so here's the question

each year, 21% of the medicinal plants grown at a botanical park are sold to pharmaceutical companies, and 110 replacements are planted. If there are 680 plants this year, how many medical plants will the park have in 4 years, assuming this pattern continues?

thanks, I think I'm just doing it wrong because I get a different answer each time!

Answer 1

1st year: 680 - 0.21(680)+110= 680-143+110=647
2nd year: 647-0.21(647)+110= 647-136+110=621
3rd year: 621-0.21(621)+110= 621-131+110=600
4th year: 600-0.21(600)+110= 600-126+110=584

Answer 2

I believe the answer is 571 plants at the end of 4 years (after the sale when the 110 replacements are planted).

Here's the formula:

Yr #1(x) - 21%(x) = z (plants left after sale); x=680
Yr #2 = (z +110) - 21%(z+110) = a (plants left after sale); z=537
Yr #3 = (a +110) - 21%(a+110) = b (plants left after sale); a=490
Yr#4 = (b+110) - 21%(b+110) = c (plants left after sale); b=474
c = 461+110 = 571 plants after 4 years.

Yr#1 = 680 (before sale); 647 (after sale w/ planting)
Yr#2 = 647 (before sale w/ planting); 600 (after sale w/ planting)
Yr#3 = 600 (before sale w/ planting); 584 (after sale w/ planting)
Yr#4 = 584 (before sale w/ planting); 571 (after sale w/ planting)