5th Grade math
posted by Lucy on .
Working Backwards:
In the 1980's the Northen White Rhinoceros population decreased by 485 from what it was in the 1970s. By the 1990s the population increased 2 more than twice the population in the 1970s By the 2000s the population dropped 25 rhinoceroes to about 7 today what was the population in the 1970s

call the population in the seventies X
then in the eighties it was (X485)
in the nineties it was 2+2X +(X485) {I am taking the English here literally that the population "INCREASED" an amount 2+2X over what it was in the eighties. I hope you do not have a typo and it should be "INCREASED TO"}
in 2000s 2+2X +X  485 25 = 7
so there is your equation to solve for X 
500

(7+252)/2+485=500