Wykonajmy obliczenia.

a)

Wykonujemy mnożenie "po kawałku":

$48\cdot 50=\underline{48}\cdot 5\cdot 10=\stackrel{40\cdot 5+8\cdot 5}{\overbrace{\underline{\left(40+8\right)}\cdot 5}}\cdot 10=\left(200+40\right)\cdot 10=240\cdot 10=2400$

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b)

$122\cdot 50=\underline{122}\cdot 5\cdot 10=\stackrel{100\cdot 5+20\cdot 5+2\cdot 5}{\overbrace{\underline{\left(100+20+2\right)}\cdot 5}}\cdot 10=\left(500+100+10\right)\cdot 10=610\cdot 10=6100$

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c)

  $648\cdot 50=\underline{648}\cdot 5\cdot 10=\stackrel{600\cdot 5+40\cdot 5+8\cdot 5}{\overbrace{\underline{\left(600+40+8\right)}\cdot 5}}\cdot 10=\left(3000+200+40\right)\cdot 10=3240\cdot 10=32400$

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d)

$50\cdot 868=10\cdot 5\cdot \underline{868}=10\cdot 5\cdot \stackrel{5\cdot 800+5\cdot 60+5\cdot 8}{\overbrace{\underline{\left(800+60+8\right)}}}=10\cdot \left(4000+300+40\right)=10\cdot \left(4340\right)=43400$