12
Step-by-step explanation:
12-n/2=6
-n/2= -6
n/2=6
n=12
41
Step-by-step explanation:
Lets say blue marbles are B and yellow marbles are Y .
We know Y is twice B plus one, so Y = 2*B + 1
We also know that there are 61 marbles in total and there are only blue and yellow marbles, so
Y + B = 61 .
But wait, disnt we say Y = 2*B+1 ? Then we can rewrite that to:
2*B + 1 + B = 61
If we remove 1 from both sides, we get:
2*B + B = 60
Since 2*B = B+B, we know that B+B+B would be 3*B
So now we have 3*B = 60.
We divide both sides by 3 and we get B = 20
And then we go way back to Y being twice B plus one.
If B is 20, twice B would be 40. Plus one, 41.
So Y = 41
P.S. I found this on the internet!