a, Ta có: 24 = 2 3 . 3 ; 10 = 2.5
=> ƯCLN(24;10) = 2
BCNN(24;10) = 2 3 . 3 .5 = 120
b, Ta có: 150 = 2 . 3 . 5 2 ; 84 = 2 2 . 3 . 7
=> ƯCLN(150;84) = 2.3 = 6
BCNN(150;84) = 2 2 . 3 . 5 2 . 7
c, Ta có: 140 = 2 2 . 5 . 7 ; 210 = 2.3.5.7; 56 = 2 3 . 7
=> ƯCLN(140;210;56) = 2.7 = 14
BCNN(140;210;56) = 2 3 . 3 . 5 . 7 = 840
d, Ta có: 105 = 3.5.7; 84 = 2 2 . 3 . 7 ; 30 = 2.3.5
=> ƯCLN(105;84;30) = 3
BCNN(105;84;30) = 2 2 . 3 . 5 . 7 = 420