\[\boxed{\mathbf{Стр.\ 50.\ }еуроки - ответы\ на\ пятёрку}\]
\[\boxed{\mathbf{9.}}\]
\[1)\ 350 + 70 =\]
\[= 350 + (50 + 20) =\]
\[= 400 + 20 = 420\]
\[35\ дес. + 7\ дес. = 42\ дес. = 420\]
\[720 - 60 = 720 - (20 + 40) =\]
\[= 700 - 40 = 660\]
\[72\ дес.\ - 6\ дес. = 66\ дес. = 660\]
\[2)\ 230 + 90 = 320\]
\[640 + 80 = 720\]
\[930 - 50 = 880\]
\[350 + 60 = 410\]
\[470 - 90 = 380\]
\[560 - 70 = 490\]
\[130 - 80 = 50\]
\[810 - 40 = 770\]
\[\boxed{\mathbf{10.}}\]
\[Запишите\ только\ ответы:\]
\[54 - 26 = 28\]
\[43 + 18 = 61\]
\[70 - 31 = 39\]
\[35 + 49 = 84\]
\[82 - 25 = 57\]