a. = 6.

300

300

= 300 

1.

a) \(125+80+375+220\)

\(=\left(125+375\right)+\left(80+220\right)\)

\(=500+300\)

\(=800\)

b) \(25.11.8.4.125\)

\(=\left(25.4\right).\left(8.125\right).11\)

\(=100.1000.11\)

\(=1100000\)

c) \(18.74+18.27-18\)

\(=18.\left(74+27-1\right)\)

\(=18.100\)

\(=1800\)

d) \(75.23+75.77-500\)

\(=75.\left(23+77\right)-500\)

\(=75.100-500\)

\(=7500-500\)

\(=7000\)

e) \(150:\left[25.\left(18-4^2\right)\right]\)

\(=150:\left[25.\left(18-16\right)\right]\)

\(=150:\left[25.2\right]\)

\(=150:50\)

\(=3\)

f) \(125.23.2.8.50\)

\(=\left(125.8\right).\left(2.50\right).23\)

\(=1000.100.23\)

\(=2300000\)

g) \(235+88+165+12\)

\(=\left(235+165\right)+\left(88+12\right)\)

\(=400+100\)

\(=500\)

h) \(71.32+71.68-1100\)

\(=71.\left(32+68\right)-1100\)

\(=71.100-1100\)

\(=7100-1100\)

\(=6000\)

i) \(6^7:6^6+4^3.2-24^0\)

\(=6+64.2-1\)

\(=6+128-1\)

\(=133\)

j) \(546-6.\left[158:\left(30+7^2\right)\right]\)

\(=546-6.\left[158:\left(30+49\right)\right]\)

\(=546-6.\left[158:79\right]\)

\(=546-6.2\)

\(=546-12\)

\(=534\)

k) \(268+147+132+253\)

\(=\left(268+132\right)+\left(147+253\right)\)

\(=400+400\)

\(=800\)

2. 

a) \(7x=707\)

\(x=707:7\)

\(x=101\)

b) \(6x+5=47\)

\(6x=47-5\)

\(6x=42\)

\(x=42:6\)

\(x=7\)

c) \(35:\left(x+1\right)=7\)

\(x+1=35:7\)

\(x+1=5\)

\(x=5-1\)

\(x=4\)

d) \(12+\left(29-3x\right)=35\)

\(29-3x=35-12\)

\(29-3x=23\)

\(3x=29-23\)

\(3x=6\)

\(x=6:3\)

\(x=2\)

e) \(2.4^x+10^1=138\)

\(2.4^x=138-10\)

\(2.4^x=128\)

\(4^x=128:2\)

\(4^x=64=4^3\)

\(\Rightarrow x=3\)

f) \(7x=140\)

\(x=140:7\)

\(x=20\)

g) \(7\left(15-x\right)+14=84\)

\(7\left(15-x\right)=84-14\)

\(7\left(15-x\right)=70\)

\(15-x=70:7\)

\(15-x=10\)

\(x=15-10\)

\(x=5\)

h) \(3^x.5-15=390\)

\(3^x.5=390+15\)

\(3^x.5=405\)

\(3^x=405:5\)

\(3^x=81=3^4\)

\(\Rightarrow x=4\)

3.

Ta có:

\(\Rightarrow n+11⋮n+1\)

\(\Rightarrow n+1+10⋮n+1\)

\(\Rightarrow10⋮n+1\) hay \(n+1\inƯ\left(10\right)=\left\{-10;-5;-2;-1;1;2;5;10\right\}\)

\(\Rightarrow\) \(n\in\left\{-11;-6;-3;-2;0;1;4;9\right\}\)

Vì \(n\in N\) nên \(n\in\left\{0;1;4;9\right\}\)

a: \(20-\left[30-\left(5-1\right)^2\right]\)

\(=20-\left[30-4^2\right]\)

\(=20-14=6\)

b: \(71+\dfrac{50}{5+3\left(57-6\cdot7\right)}\)

\(=71+\dfrac{50}{5+3\cdot\left(57-42\right)}\)

\(=71+\dfrac{50}{5+3\cdot15}=71+\dfrac{50}{50}=72\)

c: \(4\cdot\left\{270:\left[50-\left(2^5+45:5\right)\right]\right\}\)

\(=4\cdot\left\{270:\left[50-32-9\right]\right\}\)

\(=4\cdot\left\{\dfrac{270}{50-41}\right\}=4\cdot\dfrac{270}{9}=4\cdot30=120\)

d: \(411-\left[\dfrac{\left(107+3\right)}{5}-2^2\right]\)

\(=411-\left[\dfrac{110}{5}-4\right]\)

=410-22+4

=410-18

=392

e: \(450-5\left[3^2\left(7^5:7^3-41\right)-12\right]+18\)

\(=450-5\left[9\cdot\left(7^2-41\right)-12\right]+18\)

\(=450-5\cdot\left[9\cdot8-12\right]+18\)

=468-5*60

=468-300

=168

f:

\(102-150:\left[18-2\cdot\left(10-8\right)^2\right]+1018^0\)

\(=102-150:\left[18-2\cdot4\right]+1\)

\(=103-\dfrac{150}{18-8}=103-15=88\)

a = 125.64.50

= 8000.50= 400000

b = (-50025)

c = (-3034) - 1066

= (-4100)

d = (-54).(38+12-50)

= (-54). 50-50

= (-54).0 = 0

e = 85.8-35.58

= 680-2030=(-1350)

bạn tick cho mình

a: =2'30s

b: =3h34'

c: =40'26s

d: =6h23'

e: =4 ngày 14 giờ