In the fruit stand of the market, they have the following offers: 1 kg of apples + 1 kg of oranges cost € 4.30 1 kg of bananas + 1 kg of oranges cost € 3.70 1 kg of apples + 1 kg of bananas cost 3, € 60 How much does a kilo of bananas cost? Solution If we define the following variables: M = 1 Kg of Apples P = 1 Kg of Bananas N = 1 Kg of Oranges We can rewrite the statement as follows: M + N = 4.30 P + N = 3.70 M + P = 3.60 And clearing we get that M = 4.30 - NN = 3.70 - PP = 3.60 - M Where can we deduce M = 4.30 - (3.70 - P) = 4.30 - (3.70 - (3.60 - M)) M = 4.30 - 3.70 + 3.60 - M 2M = 4.30 - 3.70 + 3.60 = 4.20 M = 2.10 Substituting in the third equation we obtain that P = 3.60 - 2.10 = 1.50 And finally N = 3.70 - 1.50 = 2.20.

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Batman and Robin to the rescue ... Solution It is a chalk drawing with 3D effect by Julian Beeber.