Welcome to JavaRanch.
There may be other issues with the code, but these few lines are problematic:
int score1;
score1=a*b;
score1=in.nextInt();
if (score1!=true)
"score1" is an int - you can't compare it with a boolean (which is what "true" is); you can only compare it to another int. Also, the value of score1 is changed by two successive statements, so the first value (a*b) will be lost. I think you mean something like this:
int score1 = in.nextInt();
if (score1 != a *b)
As an aside, this forum is specifically for question about threads and synchronization (see its title). I'll move it to a more appropriate forum.