The number b in y = a · b^x that you multiply by each time the input rises by one; b = 1+r with r the rate as a decimal (b>1 growth, 0<b<1 decay). The trap: the growth factor is what REMAINS, not what is lost — a 12% decrease gives b = 0.88, and the distractor uses 0.12, confusing "decreases by 12%" with "decreases to 12%."