arc4random on Xcode for C

I want to do a multiplications quiz using random numbers from 2 variables. I tried to use this:

 int answ

 int rand1= (arc4random()%10)+1;

 int rand2= (arc4random()%20)+1;

 printf("\n¿What is %d * %d?: ", rand1, rand2);

 scanf("%d", &answ);

 if (answ==rand1*rand2)
     printf("\nCorrect answer!");
 else
     printf("\Incorrect answer, the result was %d", rand1*rand2);

My problem is that both random numbers does not change when the next question is asked. I also tried adding srand(time(NULL)) and the same.. (I already have the library stdlib.h added)

What´s missing?