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Đáp án đúng là:
(600 + 30) + 5 = 600 + (30 + 5)
(600 x30) x 5 = 600 x ( 30 x 5)
\(\dfrac{30-x}{30}=\dfrac{8}{15}\)
\(\Rightarrow\left(30-x\right)15=30\times8\)
\(\Rightarrow\left(30-x\right)15=240\)
\(\Rightarrow30-x=240:15\)
\(\Rightarrow30-x=16\)
\(\Rightarrow x=30-16\)
\(\Rightarrow x=14\)
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\(\dfrac{x+30}{72}=\dfrac{5}{8}\)
\(\Rightarrow\left(x+30\right)8=5\times72\)
\(\Rightarrow\left(x+30\right)8=360\)
\(\Rightarrow x+30=360:8\)
\(\Rightarrow x+30=45\)
\(\Rightarrow x=45-30\)
\(\Rightarrow x=15\)
\(\dfrac{30-x}{30}\) = \(\dfrac{5}{15}\)
\(\dfrac{30-x}{30}\) = \(\dfrac{1}{3}\)
30 - \(x\) = \(\dfrac{1}{3}\) \(\times\) 30
30 - \(x\) = 10
\(x\) =30 - 10
\(x\) = 20
\(\dfrac{x+30}{72}\) = \(\dfrac{5}{8}\)
\(x+30\) = \(\dfrac{5}{8}\) \(\times\) 72
\(x+30\) = 45
\(x\) = 45 - 30
\(x\) = 15
\(\frac{24\times14\times30}{28\times12\times60}\)
\(=\frac{24}{12}\times\frac{28}{14}\times\frac{60}{30}\)
\(=2\times2\times2\)
\(=8\)
a,
36 x 40 = (36 x 4) x 10 = 144 x 10 = 1 440
72 x 60 = (72 x 6) x 10 = 432 x 10 = 4 320
89 x 50 = (89 x 5) x 10 = 445 x 10 = 4 450
b,
450 x 70 = (45 x 7) x 100 = 315 x 100 = 31 500
2300 x 500 = (23 x 5) x 10 000 = 115 x 10 000 = 1 150 000
17 000 x 30 = (17 x 3) x 10 000 = 510 000
= ( 60 + 50+40+30+20+10 ) x 2000 + 1500
= 210 x 2000 + 1500
= 420000 + 1500
= 421500
a/30.x=2280040
30.x=570
x=570:30=19
b/(x.30):40=840
x.30 =840.40
x.30 =33600
x =33600:30=1120
c/37200:x=60.5
37200:x=300
x=37200:300=124
d/(72000:x):60=5
72000:x =5.60
72000:x =300
x =72000:300=240
= 45 000 000 k đi
= 450,000,000 nha