Area of Triangles
Area of a triangle = ½(Base × Height)
Area of a parallelogram = Base × Height
The area of a triangle is half the area of a parallelogram on the same base and between
the same parallels.
Triangles on the same base and between the same parallels are equal in area.
A median divides a triangle into two triangles of equal area.
If a triangle and a parallelogram are on equal bases and between the same parallels, then the area of the triangle is half of the area of the parallelogram.
If two triangles are on the equal bases and between the same parallels, then they are equal in area.
The areas of triangles with the same vertex and bases along the same line are in the ratio of their bases.
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Q1
In the following parallelogram ABCD, X and Y are the midpoints of AB and CD respectively. If the area of ADYX = 36 cm^{2}, then the area of Δ BCD is equal to
Marks:1Answer:
36 cm^{2}.
Explanation:
As X and Y are the midpoints of AB and CD.
So, area of ADYX = 1/2 area of ABCD
Since the area of a triangle is half the area of a parallelogram on the same base and between same parallels, we get
area of DBCD = 1/2 area of ABCD
Hence, area of DBCD = area of ADYX = 36 cm^{2}.

Q2
If AD is a median of a triangle ABC and G is the midpoint of median AD, then ar(BGC) is equal to
Marks:1Answer:
2 ar( Δ AGC).
Explanation:

Q3
In the following trapezium PQRS, if the area of POQ is 100 cm^{2}, then the area of SOR (in cm^{2}) is
Marks:1Answer:
100
Explanation:
Since triangle PQR and triangle QRS lie on the same base QR and between same parallel PS, therefore,
area(PQR) = area (QRS) ...(1)
On subtracting area (QOR) from both sides of equation (1), we get
area (PQR)  area (QOR) = area (QRS)  area (QOR)
area(POQ) = area(SOR)
So, the area of SOR = 100 cm^{2}

Q4
In a ΔABC, AD is the median. If area of ΔABD is 156 cm^{2}, then the area of ΔADC (in cm^{2}), is
Marks:1Answer:
156
Explanation:
AD is median of ABC.
We know a median divides a triangle in two parts with equal areas.
ar( ABD) = ar(ADC) Since ar(ABD) = 156 cm^{2}, we get ar(ADC) = 156 cm^{2} 
Q5
P is any point lying on the side DC of a parallelogram ABCD. If the area of Δ APB is 125 cm^{2} and the side AB is 25 cm, then the distance between the sides AB and CD (in cm) is
Marks:1Answer:
10
Explanation:
^{}
ABCD is a parallelogram.
ar(ABCD) = 2 ar(APB) [ar(APB) = 125 cm^{2})]
(They lie on same base AB and in between same parallels AB and DC)
ar(ABCD) = 2 x 125 cm^{2} = 250 cm^{2}
Also, ar(ABCD) = base x height [base AB = 25 cm]
So, we have
Height = ar(ABCD)/base = 250/25 = 10 cm