a) (153 + 247) + ( 91 + 207 )
= 400 + 298
= 698.
b) (25.4).(125.8).15
=100.1000.15
=1500000
c) 21+23+25+...+99
= \(\frac{\left[\left(99-21+1\right):2\right].\left(99+21\right)}{2}=2370\)
d) 136.68+16.68.4
=48.(136+16.4)
=48.200
=9600
Ta có:
a) 153 + 91 + 247 + 207
= ( 153 + 247 ) + ( 91 + 207 )
= 400 + 298
= 698
b) 25 x 15 x 8 x 4 x 125
= ( 125 x 8 ) x ( 25 x 4 ) x 15
= 1 000 x 100 x 15
= 1 500 000
c) 21 + 23 + 25 + .... + 99
= ( 99 + 21 ) + ( 97 + 23 ) + ( 95 + 25 ) + ......
= 120 + 120 + 120 + .....
= 20 x 120
= 2 400
d) 136 x 68 + 16 x 272
= ( 100 + 36 ) x 68 + 16 x ( 200 x 72 )
= 100 x 68 + 36 x 68 + 16 x 200 + 16 x 72
= 6 800 + 2 448 + 3 200 + 1 152
= ( 6 800 + 3 200 ) + ( 2 448 + 1 152 )
= 10 000 + 3 600
= 13 600
a)153+91+247+207
=(153+247)+91+207
=400+91+207
=491+207
=698
Vậy 153+91+247+207=698
b)25.15.8.4.125
=(25.4).15.(8.125)
=100.15.1000
=(100.1000).15
=100000.15
=1500000
Vậy25.15.8.4.125=1500000
c)21+23+25+...+99
Dãy trên có:(99-21):2+1=40(số hạng)
=>21+23+25+...+99 = (99+21).40:2 = 2400
Vậy 21+23+25+...+99=2400
-Mk chỉ làm dc vậy thôi-
~Bn nào thấyđúng thì tk nha~
