Given The Sequence:

[kuiperbelt]

x + 56, x, 2x - 84, y

Evaluate y

[JJ109]

-84

[JJ109]

Subtracting 56 each time
x + 56 less 56 = x
Next in sequence = x - 56 but this = 2x -84
Therefore x = 28 and the number in the sequence = -28
Next number = -28 - 56 = - 84
Y = -84

Numbers in the sequence are therefore
84, 28, -28, -84

[ClareTG0ld]

I agree with JJ's logic but this is a badly-posed question as it could equally well fit with a geometric sequence (or two).

eg:
- let x = 56, then the sequence is 112, 56, 28 (half each time), suggesting y = 14;
- or let x = -84, then the sequence is -28, -84, -252 (times three each time), suggesting y = -756.

Or you could go even more exotic, letting x = 42 for a sequence of 98,42,0 (decreasing by successively smaller multiples of 14), making y = -28...

I am sure that JJ's solution is the intended one, but without more information (were we told for certain that this is an arithmetic sequence?) then you could quote any value for y you liked and be able to justify it.

[bobbinwales]

IMHO I don't think 3 items in a seqeunce like this is enough to see or justify a pattern.

[bobbinwales]

Where wasthis question from please kuiperbeltas it don't seem right as it is to me