BT1 : Tính nhanh nếu có thể : 

a) -25 + 8 + 12 + 25

b) -87 + ( -750 ) + 2018 - 13 + 750

c) ( 45 + 12 - 13 ) - ( 45 - 13 + 12 ) 

d) -15 x 56 + 43 x ( -15 ) - 15

e) -62 x 32 - 65 x 47 - 21 x 65

g) 24 x ( 16 - 5) - 16 x ( 24 - 5 ) 

h) 5 - 10 + 15 - 20 + ............+ 2015 - 2020

BT3 : Tìm n thuộc Z biết :

a) 3n + 2 chia hết n - 1

b) n mũ 2 + 5 chia  hết n+1 

c) n + 1 chia hết n mũ 2 - 2

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50+51+52+53+54+56+57+58+59+60+61+62+63+64+65+66+67+68+69+70=?

Tính nhanh

24.(16-5) +16.(24-5)

b) 31.(-18) +31.(-81) - 31

c) 13.(23+22) -3 . (17+ 28)

d) 11/53+(32/47+-10/53)+-64/94+1/-53+1/3

e) (-1+45/115+47/51)+(-9/23+-1/3)

f) -13/15+(-4/5+7/18)+-5/12+1/16

Ai giúp mk vs ạ cảm ơn nhiều ạ ( mk cần nộp gấp ạ)

bài 1, tìm x ; 

a, -16 + 23 + x = -16 

b, 2x-35=15

c, 3x+17==12

d, |x-1|=0

e, -13.|x|=-26

bài 2; tính hợp lí ;

a, 35.18-5.7.28

b, 45-5.[12+9]

c, 24. [16-5]-16.[24-5]

d, 29.[19-13]-19.[29-13]

e, 31. [-18]+31. [-81]-31

g, [-12].47+[-12].52+[-12]

f, 13. [23+22]-3.[17+28]

h, -48 + 48. [-78]+48.[-21]

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50=?

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50.

Tính hợp lý 

a. 35.18 - 5.7.28

b. 45 - 5.(12 + 9)

c. 24.(16-5) - 16.(24-5)

d. 29.(19-13) - 19.(29-13)

e. 31.(-18) + 31. (-81) - 31

g. (-12).47 + (-12).52 + (-12)

h. 13.(23+22) - 3.(17+28)

i. -48 + 48.(-78) + 48. (-21)