1 +3 +5 +7 +9 + . . . + 19 + x X 3 =724
1 + 3 + 5 + 7 + 9 + ...... + 19 + X x 3 = 724
Tìm x;biết:
1+3++5+7+9+.......+19+Xx3=724
X=
1+3+5+7+9+... ... +19+xx3=724
1 + 3 + 5 + 7 + 9 + .. .. + 19 + x x3
3 + 4 + 5 + 6 + 7 + 8 + 9 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 0 x 3 x 3 x 3 x 3 x 3 x3 x3 x3 x3 x33 x3 x3 x3 =
tính nhanh
(8x7-16-5x8)x (1+2+3+4+5+6+7+8+9)
1+3+5+7+9+11+13+15+17+19
x = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 .
x = 2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20 .
x = 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 .
Đặt tính rồi tính
16 427 + 8 109
93 680 – 7 2451
724 x 5
21847 : 7