3.61:5*100 = (3.61*100):5 = 361:5 = 72.2
Step 1: We make the assumption that 5 is 100% since it is our output value.
Step 2: We next represent the value we seek with $x$.
Step 3: From step 1, it follows that $100\%=5$.
Step 4: In the same vein, $x\%=3.61$.
Step 5: This gives us a pair of simple equations:
