Two sandwiches and a juice cost £3.40. Four sandwiches and three juices cost £7.20. Find the cost of a sandwich.
2s + j = 3.4 and 4s + 3j = 7.2.
Creating a common multiple of s gives 4s + 2j = 6.8 and 4s + 3j = 7.2.
Elimination of s gives j = 0.4, or 40p.
Substituting this back into equation 1 gives 2s + 0.4 = 3.4.
Subtracting 0.4 from each side simplifies to 2s = 3, and dividing by 2 gives s = 1.5, or £1.50.