Rachel buys three identical bags of sweets and five cans of drink, the total cost of these items came to £4.90. Rosie buys just one bag of sweets and three cans of drink and pays £2.70. What is the cost of a bag of sweets? 
Overseas Competition->Knowledge Point->Calculation Modules->Basic Concepts of Equation->Equivalent Substitution->Addition and Subtraction of Equations