5. A village has 4000 literate people in the year 2010 and this number increases by 400 per year. How many literate people will be there till the year 2020 ? Find a formula to know the number of literate people after n years ?
Sol. Since the no. of literate people increases by 400 every year, the population of literate people every year forms an A.P.
No. of people in the year 2010 (a) = 4000
Increase in population every year (d) = 400
No. of years from 2010-2020 (n) = 10
tn = a + (n – 1) d
∴ t10 = 4000 + (10 – 1) 400
∴ t10 = 4000 + 9 (400)
∴ t10 = 4000 + 3600
∴ t10 = 7600
∴ There will be 7600 literate people till the year 2020
tn = a + (n – 1) d
∴ tn = 4000 + (n – 1) 400
∴ tn = 4000 + 400n – 400
∴ tn = 3600 + 400n
