Online Course Discussion Forum

Math Challenge II-B Number Theory Problem 7.28

 
 
Picture of Laura Wu
Math Challenge II-B Number Theory Problem 7.28
by Laura Wu - Thursday, 27 April 2017, 12:11 PM
 

Hi, I am having trouble figuring out this problem. Can someone please give some hints? Thanks a lot!

 
Picture of John Lensmire
Re: Math Challenge II-B Number Theory Problem 7.28
by John Lensmire - Thursday, 27 April 2017, 1:32 PM
 

The best thing to do is to look for a pattern.

If $k=1$ we want $x\equiv 1 \pmod{2}$, so clearly $x = 1$ works.

If $k=2$ we want $x\equiv 1\pmod{2}$ and $x\equiv 2\pmod{3}$, so we can see that $x=5$ works.

If $k=3$ we want  $x\equiv 1\pmod{2}$, $x\equiv 2\pmod{3}$, and $x\equiv 3\pmod{4}$, so we can see that $x=11$ works.

I'll let you work out some more examples (try to find the smallest $x$ in each case). Then think about how:  $1$ relates to the set of numbers $\{2\}$, $5$ relates to the set of numbers $\{2,3\}$, $11$ relates to the set of numbers $\{2, 3, 4\}$, etc.

Let us know if you have any other questions or need more of a hint.