Mod m, m-1, and m-2 residues

The mod m m residue of the integer x x is 1,
the mod m 1 m-1 residue of the integer x x is 2, and
the mod m 2 m-2 residue of the integer x x is 3.

If m > 1 m>1 , and the value of x x is minimized, what is m + x m+x ?

18 10 16 7 13

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

We try to first find x and m:

When x has the residue 1 mod m, the for some integer k 1 k_{1} :

x 1 m \frac{x-1}{m} = k 1 k_{1}

When x has the residue 2 mod m-1, the for some integer k 2 k_{2} :

x 2 m 1 \frac{x-2}{m-1} = k 2 k_{2}

When x has the residue 3 mod m-2, the for some integer k 3 k_{3} :

x 3 m 2 \frac{x-3}{m-2} = k 3 k_{3}

Now we can minimize m first.

m has to be greater than 1, so the most minimized value of m is 2. But 2-2=0, and you can't divide by 0, so we try m=3.

Plugging in m=3 we get:

x 1 3 \frac{x-1}{3}

and:

x 2 2 \frac{x-2}{2}

and:

x 3 1 \frac{x-3}{1}

Using guess and check, we find that the minimum value of x is 4.

So the answer is 4+3= 7 \boxed{7}

If m=3, can the mod m-2 residue of an integer be 3? The residue should be less than m-2, which would make m at least 6.

Chaitanya Rao - 8 months, 1 week ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...