Efectuati:a)

3 ori 1/4
15 ori 3/5
12 ori 5/4
30 ori 4/25
7 ori 2intregi si 1/4
6 intregi si 2/3 ori 9

3×1/4 (pe 3 il amplificam cu 4, iar pe 1/4 il amplificam cu 3)
3×1/4=12×3/12=3 

15×3/5 (simplificam 15 cu 5)
15×3/5=9

12×5/4 (simplificam 12 cu 4)
12×5/4=15

30×4/25 (simplificam 30 cu 25)
30×4/25= 24/5

7×2   1/4= 7×9=63

6   2/3 ×9=20×9=180

3 × \frac{1}{4} = \frac{3×1}{4} = \frac{3}{4} = 0.75
15 × \frac{3}{5} = \frac{15×3}{5} = \frac{45}{5} = 9
12 × \frac{5}{4} = \frac{12×5}{4} = \frac{60}{4} = 15
30× \frac{4}{25} = \frac{30×4}{25} = \frac{120}{25} = 4,8
7 × 2 \frac{1}{4} = 7× \frac{2×4+1}{4} = 7× \frac{9}{4} = \frac{7×9}{4} = \frac{63}{4} = 15,75
6 \frac{2}{3} × 9 = \frac{6×3+2}{3} × 9 = \frac{20}{3} × 9 = \frac{20×9}{3} = \frac{180}{3} = 60