UPSC CDS 1 2020 Math Paper

If we suppose the complete area of the parallelogram is 8 units.
Then, Diagonal BD will divide it in 2 equal parts:
So, Area ABD= Area BCD=4 units
Further CO will divide triangle BCD in 2 equal parts:
So, Area DOC =4∕2=2 units
Now,
Given EF || AD so, AD = EF
EO will divide DOC in 2 equal parts;
∴ Area of triangle DOE=2∕2=1 unit
When DOE is cut out from the plate ABCD;
∴ Ratio of area of remaining portion of the plate to the whole =(8−1):8=7:8