a, 2/3 + 3/4 - 5/6 =17/12 - 5/6 = 7/12
b, 65,42× 3,5 : 3434,55= 228,97 : 3434,55 = 0,666...
c, [27,09+258,91] × 25,4 = 286 ×25,4= 7264,4
d,12/50 +8%+59/100+ 9%= 12/50 + 4/50 + 59/100+9/100
= 8/25 + 17/25
= 1
e, 17,6- 5,3+16,8-7,6+15,3-6,8
= (17,6-7,6 )+(5,3-15,3) + (16,8-6,8)
=10+(-10)+10
= 10
f, 3,54× 73+0,46×25+3,54×26+0,46×75+3,54
= 3.54 ×(73+26+1) + 0,46×(25++75)
= 3,54× 100+0,46×100
=354 +46
=400
g,1/2 + 5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90
= 1-1/2+ 1-1/6+ 1-1/12 + 1-1/20 + 1-1/42 +1-1/56+1-1/72+1-1/90 ( có 9 số 1)
= 9- (1-1/10)
= 81/10
=