Oblicz w pamieci:
a) \frac{4}{7} + \frac{2}{7}-\frac{4+2}{7}=\frac{6}{7}
b) \frac{7}{11} + \frac{4}{11}=\frac{7+4}{11}=\frac{11}{11}=1
c) \frac{9}{12} + \frac{5}{12}=\frac{9+5}{12}=\frac{14}{12}=1\frac{2}{12}=1\frac{1}{6}
d) \frac{13}{16} - \frac{9}{16}=\frac{13-9}{16}=\frac{4}{16}=\frac{1}{4}
e) 13\frac{7}{15} + 2\frac{2}{15}=13+2+\frac{7+2}{15}=15\frac{9}{15}=15\frac{3}{5}
f)2\frac{3}{4} + 5\frac{3}{4}=7+1,5=8,5
g)4\frac{3}{8} + 2\frac{5}{8}=4+2+\frac{3+5}{8}=6+\frac{8}{8}=6+1=7
h) 1\frac{5}{9} + 3\frac{5}{9}=1+3+\frac{5+5}{9}=4+1\frac{1}{9}=5\frac{1}{9}
i) 5\frac{11}{15} - 3\frac{2}{15}=(5-3)+\frac{11-2}{15}=2\frac{9}{15}=2\frac{3}{5}
j) 4 - 2\frac{3}{7}=3\frac{7}{7}-3\frac{3}{7}=1\frac{4}{7}
k) 2\frac{5}{11} - \frac{7}{11}=1\frac{5+11}{11}-\frac{7}{11}=1\frac{16}{11}-\frac{7}{11}=1\frac{16-7}{11}=1\frac{9}{11}
l) 6\frac{1}{9} - 5\frac{4}{9}=5\frac{10}{9}-5\frac{4}{9}=\frac{6}{9}=\frac{2}{3}