Zadanie podzielimy na części.

Łączna waga podręczników:

$\underline{\frac{53}{100}\text{kg}+\frac{61}{100}\text{kg}}+\frac{33}{100}\text{kg}=\frac{114}{100}\text{kg}+\frac{33}{100}\text{kg}=\frac{147}{100}\text{kg}$  

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Łączna waga zeszytów: 

$\underline{\frac{21}{100}\text{kg}+\frac{21}{100}\text{kg}}+\frac{21}{100}\text{kg}=\frac{42}{100}\text{kg}+\frac{21}{100}\text{kg}=\frac{63}{100}\text{kg}$  

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Łączna waga plecaka:

$\underset{\text{waga ksiąz˙ek}}{\underbrace{\frac{147}{100}\text{kg}}}+\underset{\text{waga zeszytoˊw}}{\underbrace{\frac{63}{100}\text{kg}}}+\underset{\text{waga pioˊrnika}}{\underbrace{\frac{43}{100}\text{kg}}}+\underset{\text{waga plecaka}}{\underbrace{\frac{39}{100}\text{kg}}}=$  

 

$=\frac{210}{100}\text{kg}+\frac{43}{100}\text{kg}+\frac{39}{100}\text{kg}=\frac{253}{100}\text{kg}+\frac{39}{100}\text{kg}=\frac{292}{100}\text{kg}=2\frac{{92}^{:4}}{{100}_{:4}}\text{kg}=2\frac{23}{25}\text{kg}$