Question

The first and fifth term of an A.P. of 40 terms are -29 & -15 respectively. Find the sum of all positive
terms of this A.P.
(a) 1605
(b) 1705
(c) 1805
(d) None of these
​

Answer 1

Answer:

1597.5

Step-by-step explanation:

a=-29

a+4d=-15

-29+4d=-15

4d=-15+29

=14/4

=7/2

First positive term is 10th term,

a+9d= -29+9×7/2

= -29+31.5

= 2.5

Sum of first 'n' terms of an A.P=n/2[2a+(n-1)d]

n=30 [40-10]

=30/2 [2×2.5+(30-1)7/2] [a=2.5]

=15[5 + 29×7/2 ]

=15[5+101.5]

=15×106.5

=1597.5