Question

15,10,5,.....In this A.P. sum of first 10 terms is.....

A) -75
B) -125
C) 75
D) 125​

Answer 1

Answer:

Sum of 1st 10 terms

According to the formula of Sum of a A.P.

n = no. of terms i.e., 10

a = 1st term i.e., 15

d = difference (10 - 15 = -5)

S = Sum

S = n/2{2a + (n-1)d}

=> S = 10/2{2*15 + (10-1)-5}

=> S = 5{30 + (-45)}

=> S = 5*(-15)

=> S = -75 (Ans)

hence sum of first 10 terms is -75

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Answer 2

Answer:

A)-75

Step-by-step explanation:

Here,No. of terms=10 So n=10

d=t2-t1=10-15= -5

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

=10/2[2(15)+(10-1)-5]

=5[30+(-45)]

=5[-15]

= -75