9)
= (12+13)+(1/2 + 7/2) =35 +8/2 = 25+4 = 29
10)
= (7 - 4 - 2)/15 = 1/15
11)
[tex]\it 3\dfrac{1}{2} +(3\dfrac{1}{2}+5\dfrac{3}{4}) = (3+3+5) +(\dfrac{1}{2}+\dfrac{1}{2}+\dfrac{3}{4}) =11+1+\dfrac{3}{4}=12\dfrac{3}{4}[/tex]
12) 1/6 + 1/9 + 3/8 + 1/4 = (12+8+27+18)/72 =65/72
Numitorul comun al celor paru fracții este 72.
Am amplificat fracțiile respectiv cu 12, 8, 9, 18.