I would suggest start with a loop to iterate through the numbers and add them together.
Something like:

int sum=0; //variable to accumulate the numbers
int natNum=1;
while(natNum<=10) //while loop continually iterates to your limit.
{
sum=sum+natNum; //accumulates number into the sum
++natNum; //increments number by 1
}

That's the only clue I'm giving right now...see if you can figure out the division part.

Sorry, I didn't take enough time putting that out there. It should be more like:

int sum=0; //variable to accumulate the numbers
int natNum=0;
while(natNum<=10) //while loop continually iterates to your limit.
{
sum=sum+natNum; //accumulates number into the sum
++natNum; //increments number by 1
cout<<sum<<" "<<endl; //output for testing purposes.
}

2) for numbers > 9, if it ends in 0, it is divisible by 10. If it ends in a 5, it is divisible by 5. If < 9, it isn't divisible by 10, but if it == 5, then it is divisible by 5. Done...