Math
posted by i love polka .
The average life expectancy for American men born in 1900 was 55 years. Life expectancy has increased by about .2 year for each birth year after 1900.
If this trend continues, for which birth year will the average life expectancy be 85 years?
how do u write and equation for to solve this?

Let life expenctancy = L . Let y be the number of years after 1900.
L = 55 + 0.2 y = 85
Solve that equation for y
0.2 y = 30
y = 150
That would make the birth year 2050 for a life expectancy of 85.