The formula for finding the total cost of an item including tip is:
#t = p + (p * r)#
Where:
#t# is the total price of the item: 42.35 for this problem.
#p# is the original price of the item: what we are solving for in this problem.
#r# is the rate of the tip: 21% for this problem. "Percent" or "%" means "out of 100" or "per 100", Therefore 21% can be written as #21/100#.
Substituting and solving for #p# gives:
#42.35 = p + (p xx 21/100)#
#42.35 = 1p + 21/100p#
#42.35 = 100/100p + 21/100p#
#42.35 = (100/100 + 21/100)p#
#42.35 = 121/100p#
#color(red)(100)/color(blue)(121) xx 42.35 = color(red)(100)/color(blue)(121) xx 121/100p#
#4235/color(blue)(121) = cancel(color(red)(100))/cancel(color(blue)(121)) xx color(blue)(cancel(color(black)(121)))/color(red)(cancel(color(black)(100)))p#
#35 = p#
The cost of the meal before the tip was 35.00