Question

plzz answer it urgently​

Answer 1

Step-by-step explanation:

Savings are:

200,200,200,240,280,.......up to n terms

But 200,240,280,......(n−2) terms forms an A.P

Since, sum of n terms of an AP =S

n

=

2

n

[2a+(n−1)d], where first term is a and common difference d

∴ According to question

400+

2

n−2

[2(200)+(n−2−1)40]=11040 ...... Sum =11040

⇒400+(n−2)[200+(n−3)20]=11040

⇒(n−2)[200+20n−60]=10640

⇒(n−2)(20n+140)=10640

⇒20(n+7)(n−2)=10640

⇒n

2

+5n−14=532

⇒n

2

+5n−546=0

⇒(n+26)(n−21)=0

⇒n=21

So, total time =21 months.

Answer 2

The answer was 3 years 11 months