2. จงหาผลลัพธ์
1) (-5.2 + 8) – 2.8
วิธีทำ
(-5.2 + 8) – 2.8
= (8 – 5.2) – 2.8
= 2.8 – 2.8
= 0
= 0
ตอบ 0
2) (-10.1 + 15.9) – (-3.2)
วิธีทำ
(-10.1 + 15.9) – (-3.2)
= (15.9 – 10.1) – (-3.2)
= 5.8 – (-3.2)
= 5.8 + 3.2
= 9.0
= 5.8 + 3.2
= 9.0
ตอบ 9.0
3) (9.05 – 3.7) + 12.1
วิธีทำ
(9.05 – 3.7) + 12.1
= 5.35 + 12.1
= 17.45
ตอบ 17.45
4) (8.5 – 11.9) + (-1.04)
วิธีทำ
(8.5 – 11.9) + (-1.04)
= [8.5 + (-11.9)] + (-1.04)
= [-(11.9 – 8.5)] + (-1.04)
= (-3.4) + (-1.04)
= -(3.4 + 1.04)
= -4.44
= (-3.4) + (-1.04)
= -(3.4 + 1.04)
= -4.44
ตอบ -4.44
5) (-12.6 – 4.4) + 9.9
วิธีทำ
(-12.6 – 4.4) + 9.9
= [(-12.6) + (-4.4)] + 9.9
= [-(12.6 + 4.4)] + 9.9
= (-17.0) + 9.9
= -(17.0 – 9.9)
= -7.1
= (-17.0) + 9.9
= -(17.0 – 9.9)
= -7.1
ตอบ -7.1
6) (-7.3 – 6.2) – 3.32
วิธีทำ
(-7.3 – 6.2) – 3.32
= [(-7.3) + (-6.2)] – 3.32
= [-(7.3 + 6.2)] – 3.32
= (-13.5) – 3.32
= (-13.5) + (-3.32)
= -(13.5 + 3.32)
= -16.82
= (-13.5) – 3.32
= (-13.5) + (-3.32)
= -(13.5 + 3.32)
= -16.82
ตอบ -16.82
7) -24.5 + (12.9 – 11.5)
วิธีทำ
-24.5 + (12.9 – 11.5)
= -24.5 + 1.4
= -(24.5 – 1.4)
= -23.1
= -23.1
ตอบ -23.1
8) 20.30 – (2 – 15.5)
วิธีทำ
20.30 – (2 – 15.5)
= 20.30 – [2 + (-15.5)]
= 20.30 – [-(15.5 – 2)]
= 20.30 – (-13.5)
= 20.30 + 13.5
= 33.80
= 20.30 – (-13.5)
= 20.30 + 13.5
= 33.80
ตอบ 33.80
9) -1.8 + (-10.15 – 2.4)
วิธีทำ
-1.8 + (-10.15 – 2.4)
= -1.8 + [(-10.15) + (-2.4)]
= -1.8 + [-(10.15 + 2.4)]
= -1.8 + (-12.55)
= -(1.8 + 12.55)
= -14.35
= -1.8 + (-12.55)
= -(1.8 + 12.55)
= -14.35
ตอบ -14.35
10) -5.5 + (12.4 – 3.24)
วิธีทำ
-5.5 + (12.4 – 3.24)
= -5.5 + 9.16
= 9.16 – 5.5
= 3.66
= 3.66
ตอบ 3.66