What would be the first negative term for an A. P. 121, 117, - ProProfs Discuss
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What would be the first negative term for an A. P. 121, 117, 113…?



A. 31
B. 30
C. 33
D. 32

This question is part of Arithmetic Progression
Asked by Jagran josh, Last updated: Jan 17, 2020

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2 Answers

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Answered Oct 12, 2017

A= 121

d= -4

let the first negative term be an,

s0 an<0

a+(n-1)d<0

121+(n-1)(-4)<0

121-4n+4<0

125-4n<0

so by hit and trial method,

let n=30,so 125-4n

=125-120=5,which is not less than0

again let n=31

so 125-4n=125-124=1 which is not less than 0

now,let n=32 so 125-4n=125-128= -3 hence the first negetive term is -3

now an= -3

a+(n-1)d= -3

121+(n-1)(-4)= -3

-4(n-1)= -3-121

-4(n-1)=-124

n-1=32

n=33

hence,answer is 33

1
 

jagran josh

Jagran josh

Answered Sep 17, 2017

32
1
 1

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Replied on Oct 12, 2017

Answer is 33

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