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M=3
u+v=80cm
v/(80-v)=3
(80-v)*3=v
240-3v=v
240=4v
v=60cm
u=80-60=20cm
1/f=1/60+1/20=1/15
f=15cm
Alambi answered the question on January 21, 2019 at 06:54
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