Wykonajmy obliczenia

a)

$2+\left(-6\right)=-4$  

($2$ zysku i $6$ straty daje nam $4$ straty)

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$-21+17=-4$  

($21$ straty i $17$ zysku daje nam $4$ straty)

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$-3+\left(-8\right)=-11$  

($3$ straty i $8$ straty daje nam $8$ straty)

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$7+\left(-6\right)+12=7+12+\left(-6\right)=19+\left(-6\right)=19-6=13$  

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$\underset{13}{\underbrace{15+\left(-2\right)}}+\left(-11\right)=13+\left(-11\right)=2$  

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b)

$8-12=8+\left(-12\right)=-4$   

($8$ zysku i $12$ straty daje nam $4$ straty)      

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$-14-6=-14+\left(-6\right)=-20$  

($14$ straty i $6$ straty daje nam $20$ straty)

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$-24-47=-24+\left(-47\right)=-71$  

($24$ straty i $47$ straty to łącznie $71$ straty)

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$7-\left(-8\right)=7+8=15$  

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$15-\left(-6\right)=-15+6=6+\left(-15\right)=-9$  

($6$ zysku i $15$ straty to $9$ straty)

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c)

$\underset{=-2}{\underbrace{6+\left(-8\right)}}-4=-2-4=-2+\left(-4\right)=-6$  

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$\underset{8}{\underbrace{15+\left(-7\right)}}-\left(-2\right)=8-\left(-2\right)=8+2=10$  

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$5-12-\left(-27\right)=5+\left(-12\right)+27=5+27+\left(-12\right)=32+\left(-12\right)=20$  

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$-5-\left(-13\right)+\left(-11\right)=\underset{8}{\underbrace{-5+13}}+\left(-11\right)=8+\left(-11\right)=-3$   

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$-14-6+\left(-18\right)=\underset{=-20}{\underbrace{-14+\left(-6\right)}}+\left(-18\right)=-20+\left(-18\right)=-38$