Question

Find the 20th tem from the last term of the Ap:3,8,13,....., 253.

Answer 1

Answer:

Here,

a=3     d=5       n=?       al (last term)=253

al=a+(n-1)d

253=3+(n-1)5

253-3=(n-1)5

250/5=n-1

50+1=n

51=n

So AP consists of 51 term now 20th term from last is 32 not 31 as it includes 51th term

Now,

n=51

a20=3+(51-1)5    {a20 is 20 th term from last}

a20=3+(50)5

a20=3+250