OK, let's work through this together. We're starting with 320 and we're going to multiply it by 5, which means we add 320 to itself 5 times.
Step 1: 0 + 320 = 320
Step 2: 320 + 320 = 640
Step 3: 640 + 320 = 960
Step 4: 960 + 320 = 1280
Step 5: 1280 + 320 = 1600

So, 320*5 = 1600