Question

Ramkali required Rs.2500 after 12 weeks to send her daughter to school.She saved Rs.100 in the first week and increased her weekly saving by Rs.20 every week.Find whether she willbe able to send her daughter to school after 12 weeks . What value is generated in the above situation?

Answer 1

First saving = 100
second saving =120
third saving = 140
clearly this is an A.P. series with a=100,
d=20
we are to finf the sum of 12 terms of this series
so,
sum =( n/2)*(2*a+(n-1)*d)
sum=(12/2)*(2*100+(12-1)*20)
sum=6*(200+11*20)
sum=6*(200+220)
sum=6*420
sum=2520
so she would be able to save Rs. 2520 in 12 months and therefore will be able to send her daughter to school

Answer 2

AP = 100+120+140+An

N = 12

A = 100

D = 20

An = A+(N-1)D

= 100+(12-1)20

= 100+220 = 320

The required An = 320

Then , Sn = N÷2{2A+(N-1)D}

= 12÷2 {2×100+(12-1)20}

= 6×450 = 2520

So , she will be able to send her daughter to school after 12 weeks .