Question

if a1,a2,........a24 are in AP and
a1+a5+a10+a15+a20+a24=225,
then a1+a2+.........+a24=
​

Answer 1

Step-by-step explanation:

an= a + (n-1)d.

So according to it,

a1+a5+a10+a15+a20+a24=225 can be written as:

a+a+4d+a+9d+a+14d+a+19d+a+23d=225

6a+69d=225…..(1)

Now sum of AP series is:

Sn=n/2[ 2a+(n-1)d]

so, S24= 12[2a+23d] (n=24)

Now , mutiplying and dividing by 3.

s24= 12\3[6a+69d]

From eq1 ;

s24= (12\3)*225

S24=900

Ans=900