3、
CD:AD=3 :(2+4+3)=1 :3
CD=1/3AD
AD=3CD=3CH36=18(cm)
MD=1/2AD=1/2×18=9(cm)
MC=9-6=3(cm)
4、
∠AOC=1/(1+4)∠AOB=1/5∠AOB
∠AOD=1/2∠AOB
∠COD=(1/2-1/5)∠AOB=3/10∠AOB
∠AOB=36÷3/10=120°
5、
(1)∠AON=180°-90°-∠BOM
=90°-1/2∠BOD
=90°-1/2∠AOC
=90°-1/2×50°
=65°
(2)∠DON的余角
=∠DOM
=∠BOM
=1/2∠BOD
=1/2∠AOC
=1/2×50°
=25°
6、
1÷(1/12+1/24)
=1÷3/24
=8(天)