1.Tính
a) 348,39 + 402,5 b) 700,64 --- 455,37 c) 23,48 + 6,35 --- 10,3
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348,39 + 402,5=750,89
700,64 - 455,37=245,27
23,48 + 6,35 - 10,3=19,53
k nha
tui chỉ làm phần b thôi há !
B=\(\frac{3}{4}\)+\(\frac{27}{28}\)+\(\frac{69}{70}\)+...+\(\frac{867}{868}\)=\(\frac{4-1}{4}\)+\(\frac{28-1}{28}\)+\(\frac{70-1}{70}\)+...+\(\frac{868-1}{868}\)
= 1+1+..+1 -(\(\frac{1}{4}\)+\(\frac{1}{28}\)+\(\frac{1}{70}\)+...+\(\frac{1}{868}\)) = 10 - \(\frac{1}{3}\)(\(\frac{3}{1.4}\)+\(\frac{3}{4.7}\)+\(\frac{3}{7.10}\)+...+\(\frac{3}{28.31}\))
=10-\(\frac{1}{3}\)(1-\(\frac{1}{4}\)+\(\frac{1}{4}\)-\(\frac{1}{7}\)+\(\frac{1}{7}\)-\(\frac{1}{10}\)+...+\(\frac{1}{28}\)-\(\frac{1}{30}\))=10-\(\frac{1}{3}\)(1-\(\frac{1}{30}\))=10-\(\frac{1}{3}\).\(\frac{29}{30}\)=10-\(\frac{29}{30}\)=\(\frac{271}{30}\)
T=147,35-23,48-36,12-47,35+23,48+136,12
T=(147;35-47,35)+(23,48-23,48)+(136,12-36,12)
T=100+0+100
T=200
b, 2,4 x 4,567 + 5, 433 x 2,4
= 2,4 x ( 4,567 + 5,433)
= 2,4 x 1 0
= 24
d, 20,14 x 99 + 20,14
= 20,14 x( 99 + 1)
= 20,14 x 100
= 2014
Bài 1:
a: =25+75=100
b: =60-17-43+12=12
c: =-2-18=-20
d: =-3+36-17=36-20=16
Bài 2:
a: =-102
b: =-1000
c: =12x15=180
d: =21x(-10)=-210
\(39,52-23,48+20,48-56,52\)
\(=\left(39,52-26,52\right)-\left(23,48-20,48\right)\)
\(=3-3\)
\(=0\)
\(39,52-23,48+20,48-26,52\\ =\left(39,52-26,52\right)+\left(-23,48+20,48\right)\\ =13-3\\ =10.\)
a)750,89
b)245,27
c)19,53
750,89
245,27
19,53