Posted by Jessie on .
in 1991 the life expectancy of males in certain county was 68.6 years in 1996 it was 70.9 years let t represent the life expectancy in year t and let t represent the number of years since 1991

Math 116 
bobpursley,
I know that model
life expectance= slope*time + constant is the math model here.
first thing, slope:
slope= changelifeexpatance/changetime
= (70.968.6)/(19961991)=2.3/5
life expectance= 2.3/5 * year + constant
now to find the constant:
life expectancey= 2.3/5 *t + constant where t= (year1991)
70.9=2.3/5* 5 + constant
solving for constant,
70.9=2.3 + constant
constant= 70.92.3=68.6
amazing, so now you have
lifeexpectancey=2.3/5 * t+68.6 where t is the years since 1991 
Math 116 
Jessie,
thank u