The population of goldfish in a marine farm is decreasing at the rate of 20 percent per year. the farm started with a goldfish population of 1,000. part a
create an equation that gives the number of goldfish in the nth year.

Step-by-step explanation:

 Part A:

 The equation modeling the problem is an exponential equation of the form:

 y = A (b) * ^ t

 Where,

 A: initial amount

 b: decrease rate

 t: time

 Substituting values we have:

 y = 1000 (0.80) ^ t

 Part B:

 For this case we substitute the value of y = 640 in the equation:

 640 = 1000 (0.80) ^ t

 We cleared t:

 640/1000 = (0.80) ^ t

 log0.80 ((0.80) ^ t) = log0.80 (640/1000)

 t = log0.80 (640/1000)

 t = 2 years

whatever you can spend with $11.53 or under.

step-by-step explanation:

20 - 8.47 = 11.53. take away the money he used for lunch from the starting amount of 20.