3. Tính hợp lí :
1) 1/10 + 4/10 + 9/30 + 16/40 + 25/50 + 36/60 + 49/70 + 72/80 + 81/90
2) 1 + 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128
25 x 17 + 12,5 x 83 x 2
3) _______________________________
1+ 3 + 5 + 7 +….+ 97+99
0,18 x 1230 + 0,9 x 45,67 x 2 x5310 x 0,6
4)________________________________
1 + 4 + 7 + 10 +….+ 52 + 55 -414
3. Tính hợp lí : 1) 1/10 + 4/10 + 9/30 + 16/40 + 25/50 + 36/60 + 49/70 + 72/80 + 81/90 2) 1 + 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 25 x 1
By Jasmine
Giải thích các bước giải:
3.
1) 1/10 + 4/10 + 9/30 + 16/40 + 25/50 + 36/60 + 49/70 + 72/80 + 81/90
= 1/10 + 4/10 + 3/10 + 4/10 + 5/10 + 6/10 + 7/10 + 8/10 + 9/10
= (1/10 + 4/10 + 5/10) + (3/10 + 7/10) + (4/10 + 6/10) + 8/10 + 9/10
= 10/10 + 10/10 + 10/10 + 8/10 + 9/10
= 3 + 8/10 + 9/10
= 3 + 17/10
= 47/10