Translate the written/verbal expression "twice a number x" into mathematical/symbolic notation:
Twice a quantity usually indicates to take two of the things in question; usually this indicates to multiply by 2.
Thus "twice a number x" can be written symbolically as 2x.
If this is part of a problem, say twice a number x is 6, then we can rewrite algebraically as 2x=6; dividing both sides by 2 yields x=3. And we can see that, indeed, twice the number 3 is 6 as required. In the expression "twice a number x is 6" twice indicates to multiply by 2, the multiplicand (the thing multiplied by the multiplier 2) is x, and the word "is" can be expressed by the equals sign.