Toán Lớp 5: Bài 3: Tính nhanh:
a) 167. 89 – 167. 35 + 54. 833 b) 394. 768 + 606. 769 + 394
c) ( 21- 1).(21 – 2).( 21 – 3)…..( 21 – 21) d) 3 . 27 . 8 + 4 . 35 . 6 + 2 . 38 . 12
e) A = ( 1001 + 1002 + 1003 +……. + 2009). ( 360. 87 – 360.32 – 360. 55)
f) B = 232323.79 – 797979. 23
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= 167.(89 – 35) + 54.833
= 167.54 + 54.883
= 54.(167 + 883)
= 54. 1000
= 54000
b) 394. 768 + 606. 769 + 394
= 394.(768 + 1) + 606.769
= 394.769 + 606 .769
= 769 (394 + 606)
= 769 . 1000
= 769000
= 20 . 19 . 18 …… 0
= 0
d) 3.27.8+4.35.6+2.38.12
=8.3.27+4.6.35+2.12.38
=24.27+24.35+24.38
=24(27+35+38)
=24.100=2400
A = (1001 + 1002 + 1003 + ……. + 2009). (360. 87 – 360.32 – 360. 55)
A = (1001 + 1002 + 1003 + ……. + 2009). [360. (87-32-55)
A = (1001 + 1002 + 1003 + ……. + 2009). [360.0]
A = (1001 + 1002 + 1003 + ……. + 2009) .0
= 0
f)B = 232323.79 – 797979. 23
B = 232323,79 – 797979. 23
B = 10101,23,79-10101,79,23
B = 10101,79,23-10101,79,23 (có hoặc không cũng được)
B = 0