To find a tip, you would divide the original price by 1.1 (to find what the price is, plus a 10% tip, which is represented by the .1). So, to reverse this, you will multiply $55 by 0.9 (to find what the $55 was without the tip).
55 x 0.9 = 49.5
Matt's check amount was $49.50 before the 10% tip.
