7.1 In the expression $5 * 4 * 3 * 2 * 1=0$ replace the asterisks with arithmetic operation signs $+ - \times \div$, using each sign exactly once, so that the equality becomes true (note that $2+2 \times 2=6$ ).
7.1 $5-4 \times 3: 2+1=0$.

7.1 $5-4 \times 3: 2+1=0$. 

(Note: The mathematical expression is kept as is, since it is a universal notation and does not require translation.)