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\(a,\left(-5\right)+11+\left(-15\right)+21+\left(-25\right)+31+...+\left(-95\right)+101\\ =\left[\left(-5\right)+11\right]+\left[\left(-15\right)+21\right]+\left[\left(-25\right)+31\right]+...+\left[\left(-95\right)+101\right]\\ =6+6+6+...+6\left(10\text{ số }6\right)\\ =6\cdot10\\ =60\)
\(b,3+\left(-12\right)+13+\left(-22\right)+23+\left(-32\right)+...+93+\left(-102\right)\\ =\left[3+\left(-12\right)\right]+\left[13+\left(-22\right)\right]+\left[23+\left(-32\right)\right]+...+\left[93+\left(-102\right)\right]\\ =\left(-9\right)+\left(-9\right)+\left(-9\right)+...+\left(-9\right)\left(10\text{ số }-9\right)\\ =\left(-9\right)\cdot10\\ =-90\)
\(a,\left(-5\right)+11+\left(-15\right)+21+\left(-25\right)+31+...+\left(-95\right)+101\)
\(=\left[\left(-5\right)+11\right]+\left[\left(-15\right)+21\right]+\left[\left(-25\right)+31\right]+...+\left[\left(-95\right)+101\right]\)
\(=6+6+6+...+6\) (10 số 6)
\(=6.10=60\)
\(\)
a. \(204-84:12\)
\(=204-7\)
\(=197\)
b. \(99-97+95-93+91-89+...+7-5+3-1\)
\(=\left(99-97\right)+\left(95-93\right)+\left(91-89\right)+...+\left(7-5\right)+\left(3-1\right)\)
\(=2+2+2+...+2+2\)
\(=2.25\)
\(=50\)
a, ( - 125 ) + 100 + 80 + 125 + 20
= ( - 125 + 125 ) + 100 + ( 80 + 20 )
= 0 + 100 + 100
= 200
b, 27 + 55 + ( - 17 ) + ( - 55 )
= ( 27 - 17 ) + ( 55 - 55 )
= 10 + 0
= 10
c, ( - 92 ) + ( - 251 ) + ( - 8 ) + 251
= ( - 92 - 8 ) + ( - 251 + 251 )
= - 100 + 0
= - 100
d, ( - 31 ) + ( - 95 ) + 131 + ( - 5 )
= ( - 31 + 131 ) + ( - 95 - 5 )
= 100 + ( - 100 )
= 0
a) (-125) + 100 + 80 + 125 + 20
= [(-125) + 125] + 100 + (80 + 20)
= 0 + 100 + 100
= 200
b) 27 + 55 + (-17) + (-55)
= [27 + (-17)] + [55 + (-55)]
= 10 + 0
= 10
c) (-92) + (-251) + (-8) + 251
= [(-92) + (-8)] + [(-251) + 251]
= (-100) + 0
= -100
d) (-31) + (-95) + 131 + (-5)
= [(-31) + 131] + [(-95) + (-5)]
= 100 + (-100)
= 0
\(A=47.36+64.47+15\)
\(A=47.\left(36+64\right)+15\)
\(A=47.100+15\)
\(A=4700+15\)
\(A=4715\)
\(B=27+35+65+73+75\)
\(B=\left(27+73\right)+\left(35+65\right)+75\)
\(B=100+100+75\)
\(B=275\)
\(C=37+37.15+84.37\)
\(C=37.\left(1+15+84\right)\)
\(C=37.100\)
\(C=3700\)
\(D=\frac{1}{20.21}+\frac{1}{21.22}+\frac{1}{22.23}+\frac{1}{23.24}\)
\(D=\frac{1}{20}-\frac{1}{21}+\frac{1}{21}-\frac{1}{22}+\frac{1}{22}-\frac{1}{23}+\frac{1}{23}-\frac{1}{24}\)
\(D=\frac{1}{20}-\frac{1}{24}\)
\(D=\frac{24}{480}-\frac{20}{480}\)
\(D=\frac{4}{480}=\frac{1}{120}\)
\(E=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{49.50}\)
\(E=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{49}-\frac{1}{50}\)
\(E=1-\frac{1}{50}\)
\(E=\frac{49}{50}\)
\(\text{a,}4+8+12+...+80=\frac{\left(80+4\right).20}{2}=840\)
\(b,80-76+72-68+...+8-4=\left(80+72+64+...+8\right)-\left(76+68+60+4\right)\)
\(=\frac{\left(80+8\right).10}{2}-\frac{\left(76+4\right).10}{2}\)
\(40\)
Câu c tương tự câu b
a, =(-23) +84= 61
b, =(-12) -9=-21
c, = (-95) +95 -58
= -58
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