( x + 1 ) + ( x + 2 ) + ... + ( x + 98 ) + ( x + 99 ) = 9900
( x + x + ... + x + x ) + ( 1 + 2 + ... + 98 + 99 ) = 9900
99.x + \(\frac{\left(99+1\right).99}{2}\)= 9900
99.x + 4950 = 9900
99.x = 9900 - 4950
99.x = 4950
x = 4950 : 99
x = 50
2 . x + 5 . x - 3 . x = 125 : 4 + 27 : 3
x . ( 2 + 5 - 3 ) = 31,25 + 9
x . 4 = 40,25
x = 40,25 : 4
x = 10,0625
1)
x * ( 2 + 5 - 3 ) = 31,25 + 9
x * 4 = 40,25
x = 40,25 : 4
x= 10,0625
2 )
( x + x + x + .......... + x ) + ( 1 + 2 + ............... + 99) = 9900
Số các số hạng là :
( 99 - 1 ) : 1 + 1 = 99 số
Tổng dãy số là ;
( 99 + 1 ) x 99 : 2 =4950
Ta có : x * 99 + 4950 = 9900
x * 99 = 9900- 4950
x * 99 = 4950
x = 4950 :99
x = 50
a) \(2\times x+5\times x-3\times x=125\div4+27\div3\)
\(\Leftrightarrow\left(2+5-3\right)\times x=31,25+9\)
\(\Leftrightarrow4\times x=40,25\)
\(\Leftrightarrow x=40,25\div4\)
\(\Leftrightarrow x=10,0625\)
Vậy x = 10,0625
b) \(\left(x+1\right)+\left(x+2\right)+...+\left(x+98\right)+\left(x+99\right)=9900\)
\(\Leftrightarrow\left(x+x+...+x+x\right)+\left(1+2+...+98+99\right)=9900\)
\(\Leftrightarrow99x+\frac{\left(99+1\right)\times99}{2}=9900\)
\(\Leftrightarrow99x+4950=9900\)
\(\Leftrightarrow99x=9900-4950\)
\(\Leftrightarrow99x=4950\)
\(\Leftrightarrow x=4950\div99\)
\(\Leftrightarrow x=50\)
Vậy x = 50
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