19: \(\left(-17\right)+7-10\)
\(=\left(-17+7\right)-10\)
=-10-10
=-20
20: \(\left(-18\right)+10+8\)
\(=\left(-18\right)+\left(10+8\right)\)
=-18+18
=0
21: \(\left(-20\right)+15+5\)
\(=\left(-20\right)+\left(15+5\right)\)
=-20+20
=0
22: \(\left(-16\right)+8+8\)
\(=\left(-16\right)+\left(8+8\right)\)
=-16+16
=0
23: \(\left(-6\right)+3-3\)
\(=\left(-6\right)+\left(3-3\right)\)
=-6+0
=-6
24: \(13+3-16\)
\(=\left(13+3\right)-16\)
=16-16
=0
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