\[\boxed{\text{Страница}\text{\ 47.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\boxed{149.}\]
\[\boxed{150.}\]
\[(68 + 36) + 48 =\]
\[= (36 + 48) + 68 =\]
\[= (68 + 48) + 36\]
\((1700 + 624) + 3715 =\)
\[= (1700 + 3715) + 624 =\]
\[= (3715 + 624) + 1700\]
\[\boxed{151.}\]
\[(a + b) + c = (a + c) + b =\]
\[= (b + c) + a\]
\[\boxed{152.}\]
\[(2 \cdot 46) \cdot 5 = (2 \cdot 5) \cdot 46\]
\[(30 \cdot 9) \cdot 3 = (30 \cdot 3) \cdot 9\]
\[\boxed{153.}\]
\[При\ любых\ значениях\ k,\ a\ и\ \text{x\ }\]
\[верно\ равенство:\]
\[(a \cdot k) \cdot x = k \cdot (a \cdot x)\ \]
\[\boxed{154.}\]
\[20 \cdot 9 \cdot 5 = 900\]
\[3 \cdot 30 \cdot 4 \cdot 2 = 720\]
\[25 + 96 + 75 + 4 = 200\]
\[108 + 2 + 265 + 35 = 410\]