Question

( 1 + 2 + 3 + 4 + 5 + 6 +... + 999 + 1000 ) * (  0,75 * 0,4 - 3/4 *0,3 )

Answer 1

\(\left(1+2+3+4+5+6+...+999+1000\right)\times\left(0.75\times0.4-\dfrac{3}{4}\times0.3\right)\)

\(=\dfrac{\left(1000+1\right)\times1000}{2}\times\left[0.75\times\left(0.4-0.3\right)\right]\)

\(=500500\times0.75\times0.1=375375\)

Answer 2

Giải:

\(\left(1+2+3+4+5+6+...+999+1000\right).\left(0,75.0,4-\dfrac{3}{4}.0,3\right)\) 

Số số hạng \(\left(1+2+3+4+5+6+...+999+1000\right)\) là:

              \(\left(1000-1\right):1+1=1000\) 

Tổng dãy \(\left(1+2+3+4+5+6+...+999+1000\right)\) là:

              \(\left(1+1000\right).1000:2=500500\) 

\(\Rightarrow\left(1+2+3+4+5+6+...+999+1000\right).\left(0,75.0,4-\dfrac{3}{4}.0,3\right)\) 

\(=500500.\left[0,75.\left(0,4-0,3\right)\right]\) 

\(=500500.\left[0,75.0,1\right]\) 

\(=500500.0,075\) 

\(=37537,5\)

Answer 3

=(1000+1)×10002×[0.75×(0.4−0.3)]=(1000+1)×10002×[0.75×(0.4−0.3)]