Question

the fourth term of an ap is 10 if eleventh term is one more three times of the fourth term find the sum of its 25 terms
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Answer 1

Answer:

Step-by-step explanation:

a4 = 10 = a+3d....................(1)

a11 = 1+3(a4)

a+10d = 1+3*10

a+10d = 1+30

a+10d = 31.............. (2)

subtract equ 1 and equ 2

a+3d-(a+10d) = 10-31

a+3d-a-10d = -21

-7d = -21

d = 3

a+3*3 = 10

a+9 = 10

a = 1

S25 = n/2[2a+(n-1)d]

       = 25/2[2*1+(25-1)*3]

       = 25/2[2+72]

       = 25/2[74]

       = 25*37

        = 925