We assume the shopkeeper bought the appliances at the indicated prices, and that gain is computed on the basis of that cost price.
Since the base cost is the same for each appliance, the percentages can be added directly to find the percentage gain on 8000. However, the shopkeeper's total outlay was 16000, not 8000, so the final gain percentage is half of that total.
gain percent = (-4% + 8%)/2 = 2%
_____
If you want to see the actual numbers:
Loss on VCR = 4% × 8000 = 320.
Gain on TV = 8% × 8000 = 640.
Total gain on 16000 is -320 +640 = 320. As a percentage, that is ...
The order of operations is a rule that tells the correct sequence of steps for evaluating a math expression. We can remember the order using PEMDAS: Parentheses, Exponents, Multiplication and Division (from left to right), Addition and Subtraction (from left to right).
