a. 1 1/7 b. 9 4/5 c. 2 2/17 d. 3 17/19

2,4 : ( 2/4 × 3,4 )
24/10 : ( 1/2 × 34/10 )
12/5 : ( 1/2 × 17/5 )
12/5 : 17/10
12/5 × 10/17
120/50 = 2 20/50 = 2 2/5

2,4 ÷ (2/4 × 3,4)
= 24/10 ÷ (2/4 × 34/10)
= 12/5 ÷ (2/4 × 17/5)
= 12/5 ÷ 17/10
= 12/5 × 10/17
= 24/17
= 1 7/17