# How many terms of the A.P. : -15, -13, -11, ..... are needed to make the sum -55? Explain the reason.

The given AP is–

–15, –13, –11, ...

Here first term ( *a *) = –15 and the common difference ( *d *) = 2

Also given that, sum of *n* terms = –55

i.e. S *n * = –55

Hence sum of 5 terms and 11 terms of the given A. P. is –55.

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