Question 1138242
let c equal the cost for one cup of coffee.
let d equal the cost for one doughnut.
let t equal the cost of the tip.


your first equation is 2c + d + t = 1.70
your second equation is c + 2d + t = 1.65
your third equation is c + d + t = 1.30


solve the first and second equations simultaneously to get c - d = .05


solve the second and third equations simultaneously to get d = .35


since c - d = .05, then c must be equal to .4


your solution is that c = .4 and d = .35.


go back to any of the 3 equations and solve for t to get t = .55.


your solution is the price of a cup of coffee is 40 cents and the price of a doughnut is 35 cents and the tip is 55 cents.


i confirmed with all 3 original equations that this solution is correct.