Whakaoti i te (42+20):4-2*(9:3)-2*[18+3*(13-9)-5]=

$$( 42 + 20 ) : 4 - 2 \cdot ( 9 : 3 ) - 2 \cdot [ 18 + 3 \cdot ( 13 - 9 ) - 5 ] =$$

Aromātai

$$-\frac{81}{2}=-40.5$$

Ngā Upane Otinga

Tāpirihia te 42 ki te 20, ka 62.

$$\frac{62}{4}-2\times \frac{9}{3}-2\left(18+3\left(13-9\right)-5\right)$$

Whakahekea te hautanga \frac{62}{4} ki ōna wāhi pāpaku rawa mā te tango me te whakakore i te 2.

$$\frac{31}{2}-2\times \frac{9}{3}-2\left(18+3\left(13-9\right)-5\right)$$

Whakawehea te 9 ki te 3, kia riro ko 3.

$$\frac{31}{2}-2\times 3-2\left(18+3\left(13-9\right)-5\right)$$

Whakareatia te 2 ki te 3, ka 6.

$$\frac{31}{2}-6-2\left(18+3\left(13-9\right)-5\right)$$

Me tahuri te 6 ki te hautau \frac{12}{2}.

$$\frac{31}{2}-\frac{12}{2}-2\left(18+3\left(13-9\right)-5\right)$$

Tā te mea he rite te tauraro o \frac{31}{2} me \frac{12}{2}, me tango rāua mā te tango i ō raua taurunga.

$$\frac{31-12}{2}-2\left(18+3\left(13-9\right)-5\right)$$

Tangohia te 12 i te 31, ka 19.

$$\frac{19}{2}-2\left(18+3\left(13-9\right)-5\right)$$

Tangohia te 9 i te 13, ka 4.

$$\frac{19}{2}-2\left(18+3\times 4-5\right)$$

Whakareatia te 3 ki te 4, ka 12.

$$\frac{19}{2}-2\left(18+12-5\right)$$

Tāpirihia te 18 ki te 12, ka 30.

$$\frac{19}{2}-2\left(30-5\right)$$

Tangohia te 5 i te 30, ka 25.

$$\frac{19}{2}-2\times 25$$

Whakareatia te 2 ki te 25, ka 50.

$$\frac{19}{2}-50$$

Me tahuri te 50 ki te hautau \frac{100}{2}.

$$\frac{19}{2}-\frac{100}{2}$$

Tā te mea he rite te tauraro o \frac{19}{2} me \frac{100}{2}, me tango rāua mā te tango i ō raua taurunga.

$$\frac{19-100}{2}$$

Tangohia te 100 i te 19, ka -81.

$$-\frac{81}{2}$$

Tauwehe

$$-\frac{81}{2} = -40\frac{1}{2} = -40.5$$