1 + 2 + 3 + 4 + ..... + 49 + 50(có 50 số hạng)
=51 × 25 = 1275
2 . 17 . 12 + 4 . 6 . 21 + 8 . 3 . 62
= 24 . 17 + 24 . 21 + 24 . 62
= 24 . ( 17 + 21 + 62 )
= 24 . 100 = 2400
37 . 24 + 37 . 76 + 63 . 79 + 63 . 21
= 37 . (24 + 76) + 63 . (79 + 21)
= 37 . 100 + 63 . 100
= (37 + 63 ) . 100
= 100 . 100 = 10000
2020 . 43 + 2020 . 56 + 2020
= 2020 . 43 + 2020 . 56 + 2020 . 1
= 2020 . ( 43 + 56 + 1 )
= 2020 . 100 = 202000