1) 2/3 + 1,83 = 2/3 + 1 83/100 = 2/3 + 183/100 = (2 × 100 + 183 × 3)/300 = (200 + 549)/300 = 749/300 = 2 149/300
2) 6,4 - 3/20 = 6 4/10 - 3/20 = 6 4/10 - 3/20 =64/10 = 32/5 - 3/20 = (32 × 4 - 3 × 1)/20 = (128 - 3)/20 = 125/20 = 25/4 = 6 1/4
3) 9,8 * 3/10 = 9 8/10 * 3/10 = 98/10 *3/10 = 49/5 * 3/10 = 147/50 = 2 47/50
4) 7,2 : 1/100 = 7 2/10 : 1/100 = 72/10 : 1/100 = 36/5 :1/100 = 36/5 * 100 = 720