A) the growth is 56% per week. The 1.56 is multiplying the weight of the pumpkin now by the 56% to get the total weight after the 56% increase.
B) Replace P with 80 and solve for n:
80 = 25(1.56)^n
Divide each side by 25:
80/25 = 1.56^n / 25
3.2 = 1.56^n
Take the natural logarithm of both sides:
ln(3.2) = ln(1.56^n)
Remove the exponent:
ln(3.2) = n(ln(1.56)
Divide both sides by ln(1.56)
n = ln(3.2) / ln(1.56)
n = 2.6 weeks, round to 3 weeks.
C) Change 1.56 to 1.32 and redo the same calculation from B.
80 = 25(1.32)^n
80/25 = 1.32^n /25
3.2 = 1.32^n
ln(3.2) = ln(1.32^n)
ln(3.2) = n(ln(1.32)
n = ln(3.2) / ln(132)
n = 4.2, round to 4 weeks.
