5 1 per 3 – ( 1 per 10 + 2 per 15 ) : 1 per 25

5 1/3 – (1/10 + 2/15) ÷ 1/25

16/3 – (1×15/10×15 + 2×10/15×10) ÷ 1/25

16/3 – (15/150 + 20/150) ÷ 1/25

16/3 – 35/150 ÷ 1/25

16/3 – 35/150 × 25/1

16/3 – 35×25/150×1

16/3 – 875/150

16×150/3×150 – 875×3/150×3

2.400/450 – 2.625/450

-225÷9/450÷9

-25÷5/50÷5

-5÷5/10÷5

-1/2