1) 2/3+1,83; 2) 6,4-3/20; 3) 9,8*3/10; 4)7,2: 1/100

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