Math Problem : J.8 Area ratio of parallelogram and two triangles

The quadrangle ABCD in a figure is a parallelogram. QS and BC are parallel and RT and CD are also parallel.

The point P which is an intersection of QS and RT is on the diagonal line BD.

(The length of BP) : (length of PD) = 2 : 1.

Find the area ratio between the sum of the area of the triangle AQT and CSR and the area of parallelogram ABCD.












Answer
2 : 9 

Solution
In a figure, since BP : PD = 2 : 1, AT : TD = BR : RC = BQ : QA = CS : SD = 2 : 1.

Each area of parallelograms AQPT and PRCS is set to be 2 × 1 = 2.

Then, the sum of the area of △AQT and △CSR can also be set to 2.

The area of parallelogram ABCD can be set to (2+1) × (2+1) = 9.

Therefore, the area ratio is 2 : 9.