75 nhé bạn

TL :

   ( 15 x 15 ) : 2 x ( 15 x 15 ) : 2 x ( 15 x 15 ) : 2 + ( 0 + 1 + 2 + 2 + 3 + 45 ) x 0

= 0

=> vì : tất cả số nào nhân vs 0 đều = 0

_HT_

Đáp số cuối cùng bằng -4/15

(2+4+6+8+...+100) x (15x3-15x2-15)

=(2+4+6+8+....+100)x(15x(3-2-1))

=(2+4+6+8+...+100)x(15x0)

=(2+4+6+8+...+100)x0

=0

15+15*2+7*15-100

=15*(1+2+7)-100

=15*10-100

=150-100

=50

15+15*2+7*15-100=15*1+15*2+7*15-100

                             =15*(1+2+7)-100

                             =15*10-100

                              =150-100

                             =50

\(=15\times\left(2+3-5+10\right)\\ =15\times10\\ =150\)

\(15\times2+15\times3-15\times5+15\times10\)

\(=15\times(2+3-5+10)\)

\(=15\times10=150\)

\(a,21.\left(-15\right)+67.\left(-15\right)+\left(-15\right)+\left(-15\right).12\)

\(=21.\left(-15\right)+67.\left(-15\right)+\left(-15\right).1+\left(-15\right).12\)

\(=-15.\left(21+67+1+12\right)\)\(=-15.101=-1515\)

\(b,\left(-30\right)+76+30\)\(=\left(-30+30\right)+76=0+76=76\)

\(d,15.\left\{22-\left[400:\left(140+12.5\right)\right]\right\}\)

\(=15.\left\{22-\left[400:\left(140+60\right)\right]\right\}\)

\(=15.\left[22-\left(400:200\right)\right]\)

\(=15.\left(22-2\right)=15.20=600\)

a. (-15) x 101 = -1515 

b. (-30+30) +76 = 76

    15*5,5+15:0,25+25:2

=  15*5,5+15*4+15

=  15*5,5+15*4+15*1

=  15*(5,5+4+1)

=  15*10,5

=  157,5

15x5,5+15:0,25+15:2

= 15 x \(\dfrac{11}{2}\) +15 x \(\dfrac{1}{4}\) + 15 x \(\dfrac{1}{2}\) 

= 15 x (\(\dfrac{11}{2}\) + \(\dfrac{1}{4}\)+\(\dfrac{1}{2}\))

= 15 x \(\dfrac{25}{4}\)

= \(\dfrac{375}{16}\)

Gọi \(S=\frac{15}{15\cdot16}+\frac{15}{16\cdot17}+..+\frac{15}{19\cdot20}\)

\(\Leftrightarrow S=1-\frac{15}{16}+\frac{15}{16}-\frac{15}{17}+...+\frac{15}{19}-\frac{15}{20}\)

\(\Leftrightarrow S=1-\frac{15}{20}=\frac{1}{4}<\frac{1}{3}\)

Vậy S< \(\frac{1}{3}\)

--------------------Good luck------------------------