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a,87.36 + 87.64 = 87 . (64 + 36) = 87 x 100 = 8700
b, 91.51 + 49.163 - 49.72 = 91.51 + ( 49.163 - 49.72 ) = 91.51 + 49.91 = 91.(51+49) = 91.100 = 9100
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47.63 = (55 - 8)(55 + 8)
= 55² - 8²
= 3025 - 64
= 2961
--------
47.(63 - 15) - 63.(47 - 15)
= 47.63 - 47.15 - 63.47 + 63.15
= 47.(63 - 63) + 15.(63 - 47)
= 47.0 + 15.16
= 0 + 240
= 240
47.63 = (55 - 8)(55 + 8)
= 55² - 8²
= 3025 - 64
= 2961
--------
47.(63 - 15) - 63.(47 - 15)
= 47.63 - 47.15 - 63.47 + 63.15
= 47.(63 - 63) + 15.(63 - 47)
= 47.0 + 15.16
= 0 + 240
= 240
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\(c.\left[461+\left(-78\right)+40\right]+\left(-461\right)=461-78+40-461=\left(461-461\right)+\left(-78+40\right)=-38.\)
\(d.\left(53-76\right)-\left[-76-\left(-53\right)\right]=53-76+76-53=0.\)
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49 x 36 + 49 x 64
= 49 x (36+64)
= 49 x 100 = 4900
---
g, 218 x 47 + 218 x 52 + 218
= 218 x (47+1+52)
= 218 x 100
= 21800
h, 119 x 27 - 27 x 19
= 27 x (119 - 19)
= 27 x 100
=2700
f: =45(36+64)=45*100=4500
g: =218(47+52+1)
=218*100=21800
h: =27(115-15)=27*100=2700
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\(36\cdot12+12\cdot65-12\)
\(=12\cdot\left(36+65-1\right)\)
\(=12\cdot\left(35+65\right)\)
\(=12\cdot100\)
\(=1200\)
36.12+12.65-12=36.12+12.65-12.1=(36+65-1).12=100.12=1200
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a) \(198+789+502+311\)
\(=\left(198+502\right)+\left(789+311\right)\)
\(=700+1100\)
\(=1800\)
b) \(15.6.4.125.8\)
\(=\left(15.4\right).6.\left(125.8\right)\)
\(=60.6.1000\)
\(=360000\)
c) \(367+129+133+371+17\)
\(=\left(367+133\right)+\left(129+371\right)+17\)
\(=500+500+17\)
\(=1000+17\)
\(=1017\)
d) \(37.64+37.35+37\)
\(=37.\left(64+35+1\right)\)
\(=37.100\)
\(=3700\)
e) \(3.25.8+4.37.6+2.38.12\)
\(=\left(3.8\right).25+\left(4.6\right).37+\left(2.12\right).38\)
\(=24.25+24.37+24.38\)
\(=24.\left(25+37+38\right)\)
\(=24.100\)
\(=2400\)
f) \(136.48+16.272+68.20.2\)
\(=136.48+16.2.136+68.2.20\)
\(=136.48+32.136+136.20\)
\(=136.\left(48+32+20\right)\)
\(=136.100\)
\(=13600\)
g) \(1+6+11+16+...+46+51\)
Số số hạng là :
\(\left(51-1\right):5+1=11\) ( số )
Tổng là :
\(\left(1+51\right)\times11:2=286\)
Chúc bạn học tốt
91.51 + 59.163 - 49.72
= 91.51 + (10 + 49).163 - 49.72
= 91.51 + 10.163 + 49.163 - 49.72
= 91.51 + 10.163 + 49.(163 - 72)
= 91.51 + 10.163 + 49.91
= 91.(51 + 49) + 10.163
= 91.100 + 10.163
= 910.10 + 10.163
= 10.(910 + 163)
= 10.1073
= 10730