Đáp án + Giải thích các bước giải:

 bài ` 1 : `

` a, 14 xx 50 `

` = 700 `

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` b, 16 xx 125 `

` = 2000 `

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` c, 9 xx 24 xx 25 `

` = 216 xx 25 `

` = 5400 `

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` d, 12 xx 125 xx 54 `

` = 1500 xx 54 `

` = 81000 `

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` e, 30 xx 40 xx 50 xx 60 `

` = 1200 xx 50 xx 60 `

` = 60000 xx 60 `

` = 36000000 `

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` f, 64 xx 125 xx 875 `

` = 8000 xx 875 `

` = 7000000 `

bài ` 2 ` : 

` a, 27 xx 36 + 27 xx 64 `

` = 27 xx ( 36 + 64 ) `

` = 27 xx 100 `

` = 2700 `

_______________________________

` b, 25 xx 57 xx 25 + 63 - 150 `

` = 25 xx ( 57 + 63 ) - 150 `

` = 25 xx 100 - 150 `

` = 2500 - 150 `

` = 2350 `

_______________________________

` c, 425 xx 7 xx 4 - 170 xx 60 `

` = 11900 - 10200 `

` = 1700 `

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` d, 8 xx 9 xx 14 + 6 xx 17 xx 12 + 19 xx 4 xx 18 `

` = 72 xx 14 + 72 xx 17 xx 72 xx 19 `

` = 72 xx ( 14 + 17 + 19 ) `

` = 72 xx 50 `

` = 3600 `

dạng ` 5 `

bài ` 1 `: 

` a, 2 xx x + 3 = 15 `

` => 2 xx x     = 15 - 3 = 12 `

` => x            = 12 : 2 `

` => x            = 6 `

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` b, 28 - 3 xx x = 13 `

` => 3 xx x      = 28 - 13 `

` => 3 xx x      = 15 `

` => x              = 15 : 3 = 5 `

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` c, ( x - 1954 ) xx 5 = 50 `

` => x - 1954          = 50 : 5 = 10 `

` => x                     = 1954 + 10 `

` => x                     = 1964 `

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` d, 30 xx ( 60 - x ) = 30 `

` => 60 - x             = 30 : 30 = 1 `

` => x                     = 60 - 1 `

` => x                     = 59 `

bài ` 2 ` :

` a, x + 99 : 3 = 55 `

` => x + 33    = 55   ` 

` => x            = 55 - 33 `

` => x            = 22 `

_____________________________

` b, (x -25 ) : 15 = 20 `

` => x - 25        = 20 xx 15 `

` => x - 25        = 300 `

` => x                = 300 + 25 `

` => x                = 325 `

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` c, ( 3 xx x - 15 ) xx 7 = 42 `

` => 3 xx x - 15          = 42 : 7 = 6 `

` => 3 xx x                  = 6 + 15 `

` => 3 xx x                  = 21 `

` => x                         = 21 : 3 `

` => x                         = 7 `

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` d, x ( xx + 1 ) = 2 + 4 + 6 + 8 + 10 + ... + 2500 `

` => x(x+1)=2+4+6+...+ 2500 `

` => x(x+1)=(2500+2) xx 1250 : 2 `

` => x(x+1)=1563750 `

` => x(x+1)=1250 xx (1250+1) `

` => x=1250 `

` \color{lightblue}{\text{#Sunny Mery} `