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a: \(\left(\frac45-\frac{13}{20}\right):\frac35\)
\(=\left(\frac{16}{20}-\frac{13}{20}\right)\cdot\frac53\)
\(=\frac{3}{20}\cdot\frac53=\frac{5}{20}=\frac14\)
b: \(197-13\cdot8+768\)
=197-104+768
=93+768
=861
c: \(20,7+1,47:7-23\%\cdot5\)
=20,7+0,21-1,15
=19,76
d: \(\frac{21}{77}\cdot\frac12+\frac{4}{11}\cdot\frac16+\frac{5}{11}\cdot\frac13\)
\(=\frac{3}{11}\cdot\frac12+\frac{2}{11}\cdot\frac13+\frac{5}{11}\cdot\frac13=\frac{3}{11}\cdot\frac12+\frac{7}{11}\cdot\frac13=\frac{3}{22}+\frac{7}{33}\)
\(=\frac{9}{66}+\frac{14}{66}=\frac{23}{66}\)
1+2+3+4+5+6+7+8+9+10=55
11+12+13+14+15+16+17+18+19+20=155
1+2+3+4+5+6+7+8+9+10+11+12+13+14 +15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30-50-53=362
\(1+2+3+4+5+6+7+8+9+10=55\)
\(11+12+13+14+15+16+17+18+19+20=155\)
\(\dfrac{13}{20}-\left(\dfrac{1}{4}-\dfrac{5}{20}\right)\)
\(=\dfrac{13}{20}-\dfrac{1}{4}+\dfrac{5}{20}\)
\(=\left(\dfrac{13}{20}+\dfrac{5}{20}\right)-\dfrac{1}{4}\)
\(=\dfrac{18}{20}-\dfrac{1}{4}\)
\(=\dfrac{9}{10}-\dfrac{1}{4}\)
\(=\dfrac{18}{20}-\dfrac{5}{20}\)
\(=\dfrac{18-5}{20}\)
\(=\dfrac{13}{20}\)
=13/20-1/4+5/20
=9/10-1/4
=18/20-5/20
=13/20