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    The number of 4-digit numbers is: (9999 - 1000): 1 + 1 = 9000 (number)
    If you do not use numbers 2 and 3, then you have eight digits left to form units, tens and hundreds. Since zeros can not be used to make thousands of digits, there are only seven digits left to make thousands. According to the kernel rule, we have: 8 x 8 x 8 x 7 = 3584 (number)
    Inference: A 4-digit number containing two digits, or three or both, is 9000 - 3584 = 5416 (number).

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    Total height of 2 boys are: 131.6 x 2 = 263.2(cm)
    Total height of 4 girls are: 128.3 x 4 = 513.2(cm)
    Total height of all children are: 263.2 + 513.2 = 776.4(cm)
    The average height of all children are: 776.4 : 6 = 129.4(cm)

                                                                           Answer: 129.4cm

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    Mai has notebooks number is :

                    3 + 4 = 7 (notebooks)

    James has notebooks is :

                    7 + 4 = 11 (notebooks)

                          Answer : 11 notebooks

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    a) 46;64

    b) We have:
    3=0+1+23=0+1+2

    6=1+2+36=1+2+3

    11=2+3+611=2+3+6

    ⇒6+11+20=37

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    We have : 3aa1 is divisible by 9

    <=> (3 + a + a + 1)  is divisible by 9

    <=> (2a + 4)  is divisible by 9

    <=>2(a + 2) is divisible by 9

    <=> a + 2 is divisible by 9

    <=> a = 7

    Answer 3771

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    Give : x−12=y+34=z−56=kx−12=y+34=z−56=k

    ⇒⎧⎪⎨⎪⎩x=2k+1y=4k−3z=6k+5⇒{x=2k+1y=4k−3z=6k+5

    Change x,y,z into 5z - 3x - 4y = 50 , we have :

    5(6k + 5) - 3(2k + 1) - 4(4k - 3) = 50

    30k + 25 - 6k - 3 - 16k + 12 = 50 

    8k + 34 = 50

    8k = 16

    => k = 2

    ⇒⎧⎪⎨⎪⎩x=2k+1=2.2+1=5y=4k−3=4.2−3=5z=6k+5=6.2+5=17

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    We have ab=bc=ca=a+b+cb+c+a=1ab=bc=ca=a+b+cb+c+a=1

    Then : ab=1⇒a=bab=1⇒a=b

                bc=1⇒b=cbc=1⇒b=c

                ca=1⇒c=aca=1⇒c=a

    Deduced : a = b = c 

    Which top post for a + b + c = 2007 => 3a = 2007 => a = 2007 : 3 = 669

    Dress a = b = c = 669

    There is something to ask good because neck one question or

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    Nick will need : 134134 +  334334 = 112112 = 5,5

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    ( x + 1 ) . ( 1 + 1999 ) = 4000

    x + 1 = 4000 : ( 1 + 1999 )

    x  + 1 = 4000 : 2000

      x + 1 = 2 

       x = 2 - 1 

      x = 1 

    Thank you 
     
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    100 +( 500 : 5) - 40 

    = 100 + 100 - 40 

    = 200 - 40 

    = 160

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    (1−12)(1−13)(1−14)...(1−12017)<=>12.23.34....20162017=1.2.3...20162.3.4...2017=12017(1−12)(1−13)(1−14)...(1−12017)<=>12.23.34....20162017=1.2.3...20162.3.4...2017=12017

    Value of the expression is 12017

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    You have : 300 = 22.3.52

    The number of integer factors 300 have is :

                          2.[(2 + 1)(1 + 1)(2 + 1)] = 36

                                   Answer : 36. good

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    Multiply the first equation with 2, the second with 1, the thirst with -1, the fourth with -1, then add all, we have   3a+2b=30+30−5−0=553a+2b=30+30−5−0=55. Therefore    6a+4b=1106a+4b=110.

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    Add all equations we have  3(r+s+t+u)=30⇒r+s+t+u=103(r+s+t+u)=30⇒r+s+t+u=10.  Compare this equation with the second equation we deduce that  t=r+st=r+s. Substitute t=r+st=r+s for the thirst equation we get   r+3s=7r+3s=7.

    By the first equation we have  {2r+s=4r+3s=7{2r+s=4r+3s=7⇔{r=1s=2⇔{r=1s=2. Substitute r=1r=1 for  the fourth equation we deduce that u=4u=4, and the second equation give us   t=3t=3. So  r=1,s=2,t=3,u=4r=1,s=2,t=3,u=4.

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    The second equation give  y=3x4y=3x4, the thirst give  z=3x2z=3x2. Subsitute these values for the first equation we have    x+3x4−3x2=4⇔x=16x+3x4−3x2=4⇔x=16. So  x=16,y=12,z=24x=16,y=12,z=24

     
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    Multiply the first equation with 2, the second with 1, the thirst with -1, the fourth with -1, then add all, we have   3a+2b=30+30−5−0=553a+2b=30+30−5−0=55. Therefore    6a+4b=1106a+4b=110.

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    Add all equations we have  3(r+s+t+u)=30⇒r+s+t+u=103(r+s+t+u)=30⇒r+s+t+u=10.  Compare this equation with the second equation we deduce that  t=r+st=r+s. Substitute t=r+st=r+s for the thirst equation we get   r+3s=7r+3s=7.

    By the first equation we have  {2r+s=4r+3s=7{2r+s=4r+3s=7⇔{r=1s=2⇔{r=1s=2. Substitute r=1r=1 for  the fourth equation we deduce that u=4u=4, and the second equation give us   t=3t=3. So  r=1,s=2,t=3,u=4r=1,s=2,t=3,u=4.

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    The second equation give  y=3x4y=3x4, the thirst give  z=3x2z=3x2. Subsitute these values for the first equation we have    x+3x4−3x2=4⇔x=16x+3x4−3x2=4⇔x=16. So  x=16,y=12,z=24

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    That worker makes 3 tools out of time is:

                              12 hours - 7 hours 30 minute = 4 hours 30 minute = 4,5 hours

    The worker makes a product time out is :  

                               4,5 : 3 = 1,5 (hours)

                                     Answer : 1,5 hours

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    That worker makes 3 tools out of time is:

                              12 hours - 7 hours 30 minute = 4 hours 30 minute = 4,5 hours

    The worker makes a product time out is :  

                               4,5 : 3 = 1,5 (hours)

                                     Answer : 1,5 hours