Bài 3:
x÷6= 94[dư 4] 108÷x=5[dư 3]
x = 6×94+4 x = [108-3]÷5
x = 568 x = 21
Bài 5:
a. 1+2+3+4+5+6+7+8+9+10
= [1+9]+[2+8]+[3+7]+[4+6]+5+10
= 10 + 10 + 10 + 10+ 5 +10
= 55
b. [128-32×4]×[1+2+3+......+99+100]
= 0 ×[1+2+3+......+99+100]
= 0
c.1+3+5+7+9+11+13+15+17+19
= [1+19]+[3+17]+[5+15]+[7+13]+[9+11]
= 20 + 20 + 20 + 20 + 20
= 100