Please help with 5th grade math word problem

Question

In the 1980's the Northern white rhinoceroses population decreased by 485 from what it was in the 1970's. By the 1990's the population increased to 2 more than twice the population in the 1970's. By the 2000's the population dropped 25 rhinoceroses to about 7 northern white rhinoceroses today. What was the northern white rhinoceros population in the 1970s?

Answer 1

Here is how you'd solve this problem. You have to work it piecemeal.

1970: let's call it R1970

1980: R1970 - 485

1990: 2 x (R1970 - 485) + 2

2000: ((2 x (R1970 - 485) + 2) - 25 = 7

Solve for R1970 using the derived equation:

((2 x (R1970 - 485) + 2) - 25 = 7

((2 x (R1970 - 485) + 2) = 7 + 25

2 x (R1970 - 485) + 2 = 32

2 x (R1970 - 485) = 32 - 2

2 x (R1970 - 485)= 30

R1970 - 485 = 30 ÷ 2

R1970 - 485 = 15

R1970 = 15 + 485

R1970 = 500

Therefore, there were 500 northern white rhinoceros population in the 1970s.