1. 1 1/4 + 3 =

1. 1 1/4 + 3 = 5/4 + 3 = 17/4 = 4,25
2. 5 3/5 – 2 1/4 = 28/5 – 9/4
= 112/20 – 45/20 = 67/20 = 3,35
3. 2 2/6 × 2 4/10 = 14/6 × 24/10
= 28/5 = 5,6
4. 1 6/9 ÷ 3 2/6 = 15/9 ÷ 20/6 = 15/9 × 6/20
= 6/12 = 0,5
5. 8 3/5 + 3,75 ÷ (3 1/2 – 1 5/6) = 43/5 + 375/100 ÷ (7/2 – 11/6)
= 43/5 + 375/100 ÷ (21/6 – 11/6)
= 43/5 + 375/100 ÷ 10/6
= 43/5 + 375/100 × 6/10
= 43/5 + 225 = 233,6
6. 15 – 7 1/8 – 0,9 × 4,6 = 15 – 57/8 – 9/10 × 46/10
= 15 – 57/8 – 414/100
= 3000/200 – 1425/200 – 828/200
= 720/200 = 3,6