1. amount of light = 10(0.4)^x, where x is in meters.
@ 1 m
amount of light = 10(0.4)^x
amount of light = 10(0.4)¹
amount of light = 4
@ 3 m
amount of light = 10(0.4)^x
amount of light = 10(0.4)³
amount of light = 0.64
2. amount remaining = (0.87)ⁿ, n = 4 days
amount remaining = (0.87)ⁿ
amount remaining = (0.87)⁴
amount remaining = 0.5729
amount remaining = 0.57
3. P(1.1)^t, P = $130, t = 5 years
coin purchased = P(1.1)^t
coin purchased = $130(1.1)⁵
coin purchased = $209.3663
coin purchased = $209.37
