Tính số A biết rằng: A × 1,25 +3,75 = 1,25 × 9
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a) \(6,25+8,75+3,75+1,25=6,25+3,75+8,75+1,25=10+10=20\)
b) \(7,15:0,5+7,15x9-7,15=7,15x\left(1:0,5+7,19-1\right)=7,15x\left(2+9-1\right)=7,15x10=71,5\)
`@` `\text {Ans}`
`\downarrow`
`a)`
`6,25 + 8,75 + 3,75 + 1,25 `
`= (6,25 + 3,75) + (8,75 + 1,25)`
`= 10 +10 = 20`
`b)`
` 7,15 \div 0,5 + 7,15 \times 9 - 7,15 `
`= 7,15 \times 2 + 7,15 \times 9 - 7,15 \times 1`
`= 7,15 \times ( 2+ 9 - 1)`
`= 7,15 \times 10`
`= 71,5`
A × 1,25 + 2,5 = 1,25 × 9
=> A × 1,25 + 2,5 = 11,25
=> A × 1,25 = 11,25 - 2,5
=> A × 1,25 = 8,75
=> A = 8,75 : 1,25
=> A = 7
A * 1,25 + 2,5 = 1,25 * 9
A * 1,25 + 2,5 = 11,25
A * 1.25 = 11,25 - 2,5
A * 1,25 = 8,75
A = 8,75 : 1.25
A = 7
\(A\times1,25+2,5=1,25\times9\)
\(\Rightarrow A\times1,25+2,5=11,25\)
\(\Rightarrow A\times1,25=11,25-2,5\)
\(\Rightarrow A\times1,25=8,75\)
\(\Rightarrow A=8,75\div1,25\)
\(\Rightarrow A=7\)
Vậy A=7
b,4,7 + (-3,4) + 5,19 + 3,4 + (-4,7)
= [ 4,7 + (-4,7)] + [(-3,4) + 3,4] + 5,19
= 0 + 0 + 5,19
= 5,19
\(\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{6}+\frac{1}{8}\right)\times\left(1,25\times0,36-3,75\times0,12\right)\)
\(=\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{6}+\frac{1}{8}\right)\times\left(1,25\times0,36-1,25\times3\times0,12\right)\)
\(=\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{6}+\frac{1}{8}\right)\times\left(1,25\times0,36-1,25\times0,36\right)\)
\(=\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{6}+\frac{1}{8}\right)\times0\)
\(=0\)
( 1/2 + 1/4 + 1/6 + 1/8 + 1/10 ) × ( 1,25 × 0,36 - 3,75 × 0,12 )
= ( 1/2 + 1/4 + 1/6 + 1/8 + 1/10 ) × 0
(3,75 : 1,25 = 3 ; 0,36 : 0,12 = 3 )
= 0
5 *x + 3,75 *x + 1,25 *x= 20
<=>x* (5+3,75+1,25) =20
<=>x* 10 =20
<=>x = 20:10
<=>x =2
1,25xX+3,75xX=10
Xx(1,25+3,75)=10
Xx5=10
X=10:5
X=2
A × 1,25 + 3,75 = 1,25 × 9
A x 1,25 + 3,75 = 11,25
A x 1,25 = 11,25 - 3,75
A x 1,25 = 7,5
A = 7,5 : 1,25
A = 6
`A × 1,25 +3,75 = 1,25 × 9`
`A × 1,25 +3,75 = 11,25`
`A × 1,25 =11,25-3,75 `
`A × 1,25 =7,5`
`A=7,5 : 1,25`
`A=6`