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( 12 - x ) x 9 = 72
( 12 - x ) = 72 : 9
( 12 - x ) = 8
x = 12 - 8
x = 4
( 12 - x ) x 9 = 72
( 12 - x ) = 72 : 9
( 12 - x ) = 8
x = 12 - 8
x = 4
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\(a,C1:\left(524-168\right):4=356:4=89\\ C2:\left(524-168\right):4=524:4-168:4=131-42=89\)
\(b,C1:72:\left(9\times4\right)=72:36=2\\C2:72:\left(9\times4\right)=\left(72:9\right):4 =8:4=2\)
\(c,C1:\left(25\times72\right):9=1800:9=200\\ C2:\left(25\times72\right):9=25\times\left(72:9\right)=25\times8=200\)
a,C1:(524−168):4=356:4=89C2:(524−168):4=524:4−168:4=131−42=89a,C1:(524−168):4=356:4=89C2:(524−168):4=524:4−168:4=131−42=89
b,C1:72:(9×4)=72:36=2C2:72:(9×4)=(72:9):4=8:4=2b,C1:72:(9×4)=72:36=2C2:72:(9×4)=(72:9):4=8:4=2
c,C1:(25×72):9=1800:9=200C2:(25×72):9=25×(72:9)=25×8=200
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C1:
a. 786 x ( 32 +68)
= 786 x 100
= 78600
b. 2904 x 15 + 2904 x 35
= 43560 + 101640
= 145200
c.436 x 72 - 436 x 42
= 31392 - 18312
= 13080
d.194 x (87-7)
= 194 x 80
=15520
e.3332 : (4x49)
= 3332 : 196
= 17
f. 72 : 9 : 8
= (72 : 9) :8
= 1
g. (15 x 24) : 6
= 360 :6
= 60
m. 25 x(36 :9)
= 25 x 4
= 100
Cách 2:
a.786 x 32 + 786 x 68
= 25152 + 53448
= 78600
b. 2904 x ( 15 + 35)
= 2904 x 50
= 145200
c.436 x (72 -42)
= 436 x 30
= 13080
d.194 x 87 - 194 x7
= 16878 - 1358
= 15520
e. 3332 : (4 x 49)
= 3332 : 4 : 49
= 833 : 49 = 17
f. 72 : 9 :8
= 72 : (9 x8)
= 72 : 72
=1
g. (15 x 24) :6
= 15 x (24 :6)
= 15 x 4
= 60
m. 25 x (36 :9)
= ( 25 x36 ):9
= 900 : 9
=100
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a: =24*1000=24000
b: =120*1000=120000
c: =72(135+65):25-140
=72*8-140=436
d: =18(957-354-621):72=-9/2
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Lời giải:
a.
$18\times 85+9\times 30=18\times 85+18\times 15=18\times (85+15)$
$=18\times 100=1800$
b.
$9\times 13+9\times 80+63=9\times 13+9\times 80+9\times 7$
$=9\times (13+80+7)=9\times 100=900$
c.
$8\times 11+16\times 40+72=8\times 11+8\times 80+8\times 9$
$=8\times (11+80+9)=8\times 100=800$
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\(a.18\times85+9\times30\)
\(\text{=}1530+270\)
\(\text{=}1800\)
\(b.9\times13+9\times80+63\)
\(\text{=}117+720+63\)
\(\text{=}900\)
\(c.8\times11+16\times40+72\)
\(\text{=}88+640+72\)
\(\text{=}800\)
(72 +X) : 9 = 9171:9
72 + X = 9171
X = 9171 - 72
X = 9099