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    Reply:

    a. The length is:

    90 .1 / 3 = 30 (m)

    The width is:

    90: 2 - 30 = 15 (m)

    b. Area is:

    30. 15 = 450 (m2)

    c. The width of the pond is:

    15: 2 = 7.5 (m)

    The length of the pond is:

    30. 1/3 = 10 (m)

    The perimeter of the pond is:

    (10 + 7,5). 2 = 35 (m2)

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    We have :

    ab + ba = 100

    <=> 2.a.b = 100

    <=> ab = 50

    So ab = 50

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    1 x 2 x 3x 4 x 5 x 6 x 7 x 8 x 9 x 10

    = (1 x 10) x (2 x 5) x 3 x 4 x 6 x 7 x 8 x 9

    = 10 x 10 x 3 x 4 x 6 x 7 x 8 x 9

    = 3628800

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    The volume of the smaller can is:

      (62)2.3,14.20=565,2(62)2.3,14.20=565,2(cm3)

    The volume of the larger volume is:

     (82)2.3,14.17=854,08(82)2.3,14.17=854,08(cm3)

    So the answer is:565,2854,08=4568

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    Tell the praction to find is 

    ⇒⎨⎩b−a=82ab−1=1⇒{b−a=82ab−1=1

    => a + a = b - 1

    => a + 1 = b - a  = 8

    => a = 7

    => b = 15

    So the fraction to find is 715

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    Tell x is the number to find

    => x(x+2) = 783

    => x = 27 or x = -29

    But x is a positive => x = 27

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    Tell the praction to find is ab

    ⇒{b−a=82ab−1=1

    => a + a = b - 1

    => a + 1 = b - a  = 8

    => a = 7

    => b = 15

    So the fraction to find is 

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    The answer is:

     

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    -5 ≤ 2x - 7 ≤ 21

    => 2 ≤ 2x ≤ 28

    => 1 ≤ x ≤ 14

    So there are: 14 - 1 + 1 = 14 numbers is true

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    The area of the circle is:

        (7:2)2.3,14=38,465(7:2)2.3,14=38,465

    The area of the square is:

       (√722)2=492(722)2=492

    So the answer is:∣∣∣38,465−492∣∣∣=|13,965|≈13,97

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    √2+4+6+x2+4+6+x (Condition −12≤x<8−12≤x<8).

    ⇔√12+x=n(n∈N)⇔12+x=n(n∈N)

    So x will satisfy x={−12;−11;−8;−3;4}x={−12;−11;−8;−3;4}

    The sum of x=−12−11−8−3+4=−30x=−12−11−8−3+4=−30

    Answer : - 30.

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    1800 = 23.32.52 = 1.1800 = 2.900 = 3.600 = 4.450 = 5.360 = 6.300 = 8.225 = 9.200 = 10.180 = 12.150 = 15.120 = 18.100 = 20.90 = 24.75 = 25.72 = 30.60 = 36.50 = 40.45         

    So we have 36 numbers                                                                                 

    1,2,3,4,5,6,8,9,10,12,15 is smaller or equal 15.

    So we have 36 - 11 = 25 numbers left

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    Tell the books is a, the CD is b

    => 3a+8b=2(a+5b)3a+8b=2(a+5b) and a+b = $45

    => 3a + 8b = 2a + 10b

    => a = 2b

    => a+b = b+2b = 3b = 45<=>b=45<=>b=15

    => a = $15.2 = $30

    => 6a = 30.6=30.6=180

    So the answer is $180

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    Call the percent increase is x (%)

    Because the number of participants increase each year study.

    We have equation : 

    {P=40+40⋅x%P+P⋅x%=90{P=40+40⋅x%P+P⋅x%=90

    ⇔{P=40+40⋅x%40+40⋅x%+(40+40⋅x%)⋅x%=90⇔{P=40+40⋅x%40+40⋅x%+(40+40⋅x%)⋅x%=90

    ⇒{P=40+40⋅x%x%=50%⇒{P=40+40⋅x%x%=50%

    So P=40+40⋅50%=60P=40+40⋅50%=60

    Answer P = 60

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    The length of this rectange is:

    (622)÷(1+4)⋅4=24,8(m)(622)÷(1+4)⋅4=24,8(m)

    The width of this rectange is:

    24,8 : 4 = 6,2 [m]

    So the area of this rectange is:

    24,8 . 6,2 = 153,76 [m2]

    Answer: 153,76m

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