Answer Q no 19,20,23 urgent briefly do on copy and paste the picture .

1
by sahilverma

2016-03-08T22:33:34+05:30

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
Sorry to say that i only know the 23 sum so i am doing that one only.

given that
sum of the first 6 terms = 42
sum n terms = n/2 [2a + (n-1) d]
here n = 6
6/2 [2a + (6-1) d] = 42
3[2a + 5d] = 42
2a + 5d = 14   -----------------(1)

then 10th term and the 30 term ratio is 1:3
so,
a + 9d / a + 29d = 1/3
3(a + 9d) = a +29d
3a +27d = a + 29d
3a-a = 29d-27d
2a = 2d
a = d ----------------(2)

from the  (1)
2a +5d = 14   from the  (2)
2a + 5a = 14
7a = 14
a = 2
then  d = 2
the first term is 2
the thirteen term = a + 12d
= 2 + 12(2)
= 2 + 24
= 26.

Good job but qns is simple go for hard.
i mean prepare difficult qns for your exam
ok