Question

The third and sixth term of a series in A.P are 13 and 31 respectively find 20th term​

Answer 1

Answer:

tn=a+(n-1)d

for t3,

t3=a+2d

13=a+2d___(1)

for t6,

t6=a+5d

31=a+5d___(2)

subtracting (1) from (2)

31=a+5d - 13=a+2d

18=3d

d=6

put the value of d in (1)

13=a+2d

13=a+2(6)

13=a+12

a=1

for t20

tn=a+(n-1)d

t20=1+(20+1)6

=1+21*6

=123