There's no missing money. Take a look at the problem carefully....
Your parents gave you 50 pesos each, if you return 1 peso to them respectively then the money you owe them altogether will be 98 pesos (49 + 49 = 98). Now, you have the remaining 1 peso with you that you got from the shopkeeper. Subtract it from the 98 pesos you have. You'll get 97 pesos, which is = to the amount you payed for the shirt. Simple!
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