Interview Question for Analyst at Fidelity Investments:

If you double your volume, while keeping the price constant, you make $800 (($10-$8)($400)) and if you double your price but loose half of your volume you make $1,200 (($20-$8)(100)). The catch is, however, that it is much easier to do the former because no one would realistically buy your good if you double the price.

I don't agree with the part that practically it is easier to double the quantity while keeping the price same.

Neither do I agree with the other side. I'd ask for more data, ask more questions before I answer that viz. if we know consumer's willingness to pay, price of substitutes available, what would it take to double the quantity sold at the same price, demand curve etc.