What effect will a decrease in price have on sales?

It really depends. If this is a basic math question, one would assume that if the price is lower, people will buy more, ie sales will increase.

However, in real life, that is true only to a point. For example, if I offered to sell you a soda for a nickel, you probably wouldn't buy it. Most likely you'd assume that it was poor quality or that I was trying to trick you. So, lowering price doesn't necessarily mean increased sales.