The sum of the 1st and 2nd terms of an A.P. is 4 and the ...
The sum of the 1st and 2nd terms of an A.P. is 4 and the 10th term is 19. Find the sum of the 5th and 6th terms.
11
20
21
22
24
Correct answer is B
Tn=a+(n−1)d (terms of an A.P)
T1=a
T2=a+d
T10=a+9d
a+a+d=2a+d=4...(i)
a+9d=19...(ii)
(ii) x 2: 2a+18d=38...(iii)
(iii) - (i) : 17d=34⟹d=2
2a+2=4⟹2a=2
a=1
T5+T6
= (a+4d)+(a+5d)
= 2a+9d
= 2(1)+9(2)
= 20
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