Question

Which term of ap 3, 15, 27, 39 dotdotdot will be 120 more than 20 first term?

Answer 1

Answer:

Step-by-step explanation:

AP:3,15,27,39 ,........

21st term = a+20d

So,. a=3

&. d= 15 -3= 12

A.T.Q

a[n]= a+20d+120

= 3+20(12)+120=363

Hence,a[n] = 363 ..........(1)

But a[n] = a+(n-1)d ...........(2)

So, from eq (1) & (2)

a+ (n-1) d= 363

3+(n-1) 12= 363. ( a= 3,d= 12)

(n-1)12= 363-3

(n-1)= 360/12

n-1= 30

n= 30+1=31

Hence, term will be 31st term which is 120 more than 21st term..