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 will be able to send her daughter to school after 12 weeks. what value is generated in the above situation

Answer 1

As given his savings are 100+120+140+................+320 is an AP
So
a1=100 , d=a2-a1=120-100=20 , n=12
Sum of series will be
Sn=n/2[2a1+(n-1)d]
Sn=12/2[2*100+(12-1)20]
Sn=6[200+220]
Sn=6[420]=2520 rupees it means yes she will be able to collect Rs. 2500.

Answer 2

required AP is 100+120+140......An
n=12
a=100
d=20
An= a+ (n-1)d
= 100+(12-1) 20
=100+11×20
=100+220
An =320
Sn=n÷2 (2a+(n-1)d)
=12÷2 (2×100+(12-1)20
=6 (200+11×20)
=6×420
= 2520
therefore she will be able to send her child to school after 12 weeks