\[Страница\ 40.\]
\[\boxed{\mathbf{10.}}\]
\[\textbf{а)}\ 42,56 - 17,798 + 20,7 =\]
\[= 63,26 - 17,\ 798 = 45,462\]
\[\textbf{б)}\ (3,07 + 4,78) - 2,09 =\]
\[= 7,85 - 2,09 = 5,\ 76\]
\[\textbf{в)}\ 34,978 - 21,4059 + 764,3 =\]
\[= 799,278 - 21,4059 =\]
\[= 777,8721\]
\[\textbf{г)}\ 30,06 - (7,085 + 8,02) =\]
\[= 30,06 - 15,105 = 14,955\]
\[\boxed{\mathbf{11.}}\]
\[\textbf{а)}\ 7234 - 72,34 + 7,234 =\]
\[= 7241,234 - 72,34 = 7168,894\]
\[\textbf{б)}\ 562,01 - 5,6201 + 56,201 =\]
\[= 618,211 - 5,6201 = 612,5909\]
\[\textbf{в)}\ 1200 + 0,012 - 1,2 =\]
\[= 1200,012 - 1,2 = 1198,812\]
\[\textbf{г)}\ 7260,43 - 726,043 + 7,26043 =\]
\[= 7267,69043 - 726,043 =\]
\[= 6541,64743\]
\[\boxed{\mathbf{12.}}\]
\[\textbf{а)}\ 35 - x = 24,675\]
\[x = 35 - 24,675\]
\[x = 10,325.\]
\[Ответ:10,325.\]
\[\textbf{б)}\ 70,8 - (x - 8,93) = 54,2\]
\[x - 8,93 = 70,8 - 54,2\]
\[x - 8,93 = 16,6\]
\[x = 16,6 + 8,93\]
\[x = 25,53.\]
\[Ответ:25,53.\]
\[\textbf{в)}\ 4,86x + 19,4x + 0,54x = 2020\]
\[24,8x = 2020\]
\[x = 2020\ :24,8\]
\[x = 20\ 200\ :248\]
\[x = 81\ \frac{112}{248} = 81\ \frac{14}{31}.\]
\[Ответ:\ \ 81\frac{14}{31}.\]
\[\textbf{г)}\ (43,2 - x) - 5,09 = 14,2\]
\[43,2 - x = 14,2 + 5,09\]
\(43,2 - x = 19,29\)
\[x = 43,2 - 19,29\]
\[x = 23,91.\]
\[Ответ:\ 23,91.\]