The first term in a sequence is -20. Every consecutive term is 15 grea

Question

The first term in a sequence is -20. Every consecutive term is 15 greater than the term that immediately preceded it. What is the value of the 120th term in the sequence?

A. 1,765
B. 1,770
C. 1,775
D. 1,780
E. 1,785

GMATinsight · Answer

First term a = -20

Common difference, d = 15

CONCEPT : nth Term of an Arithmetic Progression,  T_n = a+(n-1)*d

120th term,  = T_{120} = (-20)+(120-1)*15 = 1765

Answer: Option A

chipsy · Answer

a + 119d = -20+ 119(15)
 = -20 + (120-1)*15
 = -20 + 1800 - 15
 = 1765

Option A

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GMATWhizTeam · Answer

Solution 
 • Since the difference between any two consecutive terms of the given sequence is constant. 
 o So, the given sequence is in AP. 
• Now, the first term of the given A. P. (i.e. a) = -20
• And the common difference of the given A.P. (i.e. d) = 15
• We know that  nth term of an AP is given by the formula:
 o    a_n = a + (n-1)*d     
 • Therefore, 120th term of the given A.P. (i.e.  a_{120} )  = -20 + (120-1)*15 = -20 + 1785 = 1765    
Thus, the correct answer is  Option A.

yashikaaggarwal · Answer

nth term = dn + (a - d)
Where d is the difference between the terms = 15, 
a is the first term = -20
and n is the term number = 120

putting values = 15*120 + (-20-15)
120th term = 1800-35
120th term = 1765

Answer is A

Kinshook · Answer

Given: The first term in a sequence is -20. Every consecutive term is 15 greater than the term that immediately preceded it. 
Asked: What is the value of the 120th term in the sequence?

Sequence forms an arithmetic progression with : - 
a = -20
n = 120
d = 15

t_n = t_{120} = a + (n-1)d = -20 + 119*15 = 1765

IMO A

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The first term in a sequence is -20. Every consecutive term is 15 grea

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