What is the decimal multiplier to decrease by 15%?

Answer: 0.85

Explanation:

If we start off with $100 and decrease by 15%, then we are decreasing by $15 since 15% of 100 = 0.15*100 = 15

We start with $100 and drop to 100-15 = 85. Dividing this over the original 100 gets us 85/100 = 0.85

Put another way, 100% - 15% = 1 - 0.15 = 0.85

The decimal multiplier for "decrease by 15%" is 0.85; this sort of thing is useful if you wish to apply multiple discounts to a product.

Side note: the 0.85 can be thought of as 85%, so the product's new value is 85% of its original value