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Edwin has three flowers, one red, one blue and one yellow. They have $50$ petals in total. The blue flower has $4$ petals less than the red one and $5$ petals more than the yellow one. How many petals does the red flower have? 
Overseas Competition->Knowledge Point->Word Problem Modules->Applying Addition and Subtraction->Simple Word Problems Involving Comparing and Ordering
Blue: $(50 + 5 - 4) \div 3 = 17$  Red: $17 + 4 = 21$ 