Advanced Quant: Pattern Recognition

[MarthaM266]

In the Advanced Quant book - Page 151 - Problem 4:

What is the units digit of y?
1) The units digit of y squared equals 6
2) The units digit of (y+1)squared equals 5

The answer is B. I picked E - and can't figure how B is sufficient.

1 - leaves you with 4,6, -4, -6
2 - leaves you with -6, 4

How can they concur this is sufficient?

Thanks!

[tim]

In my book, this problem shows up on page 161, not page 151, and the problem stipulates that y is a positive integer. If your book shows this problem on page 151 OR fails to indicate that y is a positive integer, can you post a picture of the page so I can investigate the discrepancy?

[RonPurewal]

also, on this exam you will NEVER have to consider negative numbers for a problem about digits.
...or factors, or remainders, or primes, or basically anything else that's traditionally learned in a context of purely positive integers.

[RonPurewal]

also, on this exam you will NEVER have to consider negative numbers for a problem about digits.
...or factors, or remainders, or primes, or basically anything else that's traditionally learned in a context of purely positive integers.

the above ^^ is really just one case of what i stated more generally here:
https://www.manhattanprep.com/gmat/foru ... ml#p116154