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Algebra Level 4

An arithmetic progression starts with a positive odd integer. The total number of terms in the progression is odd and its middle term is greater than its first term. And for the progression, it is given that common difference 0 ( mod 2016 ) \text{common difference} \equiv 0 (\text{mod} \ 2016) . What can be commented about its last term?

It is a positive even integer It is a positive odd integer It is a negative even integer It is a negative odd integer

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2 solutions

Ashish Menon
May 27, 2016

This AP starts with a positive odd integer and it only has a single mid term. So, the number of terms in this progression is odd. Mid-term is greater than its first term so the progression is non-constant and the common difference is positive. Its common difference ( mod 2016 ) \equiv (\text{mod 2016}) indicates that the common difference is an integer divisible by 2016 2016 . Its not a negative integer as explained before. So, the common difference is a positive even integer because 2016 is even. Since the common difference is a positive integer, the number of terms in this progression is a positive odd number. Now, the last term = First term + ( Number of terms - 1 ) × Common difference = Positive odd integer + ( Positive odd integer - 1 ) × Positive even integer = Positive odd integer + ( Non- negative even integer × Positive even integer ) = Positive odd integer + Non - negative even integer = Positive odd integer \text{First term} + \left(\text{Number of terms - 1}\right)×\text{Common difference}\\ = \text{Positive odd integer} + \left(\text{Positive odd integer - 1}\right)×\text{Positive even integer}\\ = \text{Positive odd integer} + \left(\text{Non- negative even integer × Positive even integer}\right)\\ = \text{Positive odd integer} + \text{Non - negative even integer}\\ = \color{#69047E}{\boxed{\text{Positive odd integer}}}

Sparsh Sarode
May 27, 2016

1)It starts with an odd number

2)Only one mid term \rightarrow odd number of terms

3)Mid term is more than starting number \rightarrow increasing AP

4)Common difference is divisible by a even number(2016) \rightarrow common difference must be even

From 1 and 4, all the terms are odd (since, o d d + e v e n = o d d odd+even=odd )

Hence the option, last term is positive odd integer

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