Question

. If 21, a, b & -3 are in A.P , then the value of a+b is: 

15

18

5

13

​

Answer 1

Answer:

1st term=21

21+d=a

21+2d=b

4th term=21+3d= -3

=3d= -24

=d= -8

so

21-8=a

a=13

21-16=b

b=5

a+b=18

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