X=n-1 (mod n) ((n=2,..,10))
By Nikos Xasiotis on Thursday, October 11,
2001 - 06:34 pm:
Which number gives:
X mod 10=9
X mod 9=8
X mod 8=7
X mod 7=6
X mod 6=5
X mod 5=4
X mod 4=3
X mod 3=2
X mod 2=1
By Kerwin Hui on Thursday, October 11,
2001 - 08:44 pm:
First you get rid of the redundant conditions and you get
X º 8 (mod 9)
X º 7 (mod 8)
X º 6 (mod 7)
X º 4 (mod 5)
which you can now solve by Chinese Remainder Theorem, as the moduli are
pairwise coprime.
Another approach is to note that the condition given is the same as
X º -1 (mod n)
where n ranges from 2 to 10. Now apply a variation of Chinese Remainder
Theorem to get the answer.
Kerwin
By Michael Doré on Thursday, October 11, 2001 - 09:53 pm:
Or just note that X + 1 is divisible by
2,3,...,10. So it suffices for X + 1 to be divisible by just
5,7,8,9 (since then X + 1 is automatically divisible by 2,3,4,6).
So X + 1 is some multiple of 5x7x8x9.
By Yatir Halevi on Saturday, November 17,
2001 - 11:12 am:
Consider the number 10! (factorial of 10)
all the number from 1 to 10 divide 10!
Now consider the number (10!-1), This number will give a
remainder of (d-1) when divided by d, where d is any number from
2 to 10.