Mental Maths Questions and Answers: Understanding Quadrilaterals | Mental Mathematics for Class 8 PDF Download

Q1: What is the maximum number of obtuse angles that a quadrilateral can have?
Ans: 3

Q2: What is the sum of all interior angles of a hexagon?
Ans: 720º

Q3: How many non over lapping triangles can we make in a polygon having n sides by joining the vertices?
Ans: n-2

Q4: If two adjacent angles of a parallelogram are (5x — 5°) and (10x + 35°), then find the ratio of these angles.
Ans: 1:3

Q5: The angles of a quadrilateral are in the ratio 1:2:3:4. Find the difference between the smallest and the largest angle.
Ans: 108º

Q6: If PQRS is a IIgm, then find ∠Q — ∠S.
Ans: 0º

Q7: What is the number of sides of a regular polygon whose exterior angle measures 72°?
Ans: 5

Q8: If only one diagonal of a quadrilateral bisects the other, then which type of quadrilateral is it?
Ans: kite

Q9: The interior angles of a triangle are in the ratio 3:2:1, then what is the ratio of its exterior angles?
Ans: 3:4:5

Q10: If the area of a square is 289 sq.cm, then find the length of its diagonal.
Ans: 17√2cm

Q11: If a square has a diagonal of length  cm, find its area.
Ans: 864 sq. cm

Q12: How many sides does a regular polygon have if each of its interior angle is 160° ?
Ans: 18

Q13: If the sum of all interior angles of a polygon is 1080°, then how many sides does a polygon have?
Ans: 8

Q14: How many diagonals does a regular hexagon have?
Ans: 9

Q15: What is the measure of each interior angle of a regular polygon having 12 sides?
Ans: 150º

Q16: The ratio of each exterior angle to each interior angle of a regular polygon is 2:3. What is the number of sides of the polygon?
Ans: 5

Q17: The longer side of a parallelogram is 8cm. If the shorter side is 3/4 times of the longer side, then what is the perimeter of the parallelogram?
Ans: 28cm

Q18: What is the number of diagonals in a polygon of 12 sides?
Ans: 54

Q19: A polygon has 27 diagonals. How many sides does it have?
Ans: 9

Q20: In parallelogram ABCD, ∠A is greater than ∠B by 5º. What is the measure of ∠D?
Ans: 87.5º

Q21: The length of two diagonals of a rectangle are (x+3) cm and (2x-7) cm, find the value of x.
Ans: x = 10

Q22: The angles of a quadrilateral are in the ratio 1:3:4:4, then what is the sum of two greatest angles of the quadrilateral?
Ans: 240º

Q23: In a regular polygon, each interior angle is thrice the exterior angle. What is the number of sides of a polygon?
Ans: 8

Q24: The interior angle of a regular polygon is 100º more than its exterior angle. What is the number of sides of the polygon?
Ans: 9

Q25: The interior angle of a regular polygon exceeds its exterior angle by 108º. What is the number of sides of the polygon?
Ans: 10

Q26: Two adjacent angles of a parallelogram are (2x+30)° and (3x-15)°, what is the value of x?
Ans: x = 33

Q27: The lengths of the diagonals of a rhombus are 16 cm and 12 cm. what is the perimeter of the rhombus?
Ans: 40 cm

Q28: Find the value of x.

Ans: 66

Q29: Find the value of x.
Ans: x = 130

Q30: ABCD is a rhombus. If ∠ABD = 35º, find the value of x.
Ans: 55º

Q31: Find the value of  x.
Ans: 105º

Q32: ABCD is a parallelogram, Find the values of x, y and z.
Ans: x = 25, y = 45, z = 110

Q33: ABCD is a parallelogram, Find the value of  x.
Ans: x = 75

Q34: If PQRS is a rhombus, find x.

Ans: x = 4

Q35: If ABCD is a rectangle, find x.
AC = (2x - 1) cm
BD = (x + 5) cm

Ans: x = 6

Q36: ABCD is a parallelogram, BC=BE, find x.

Ans: x = 70º

Q37: ABCD is a rhombus, find the value of y-x.

Ans: 40º

Q38: ABCD is a trapezium, in which CBIIDA, CP and BP are bisectors of ∠C and ∠B respectively, find ∠A and ∠D.

Ans: ∠A= 120º,
∠D = 130º

Q39: Find x, if ABCD and PQRS are parallelograms.
Ans: x = 50

Q40: ABCD is a parallelogram, find x and y.

Ans: x = 3 units, y = 2 units

For detail explanation of solutions refer to the videos provided