8 NCERT MATH SUBJECTIVE QUESTIONS

Q1. Using the digits 4, 0 and 5, form all possible 3 digit numbers without repeating the digits. Also, classify them in a multiple of 2 and 3. Solution Digits are: 4, 0, 5 3 digit numbers are: 405, 450, 540, 504 A number is multiple of 2 if its unit place is even. Therefore, 450, 540 and 504 are multiples of 2. A number is multiple of 3 if the sum of digits is divisible by 3. For all the above 3 digit numbers, sum of digits is 9, which is divisible by 3. Hence all numbers are divisible by 3. Q2. Write all possible numbers using the digits 2, 4, 7 without repeating them. Solution All possible numbers with digits 2, 4 and 7 are: 247, 274, 427, 472, 742, 724. Q3. Write the following numbers in usual form: (i) 100 x 7 + 10 x 9 + 1 x 8 (ii) 1000 x 3 + 100 x 1 + 10 x 5 + 1 x 9 Solution (i) 100 x 7 + 10 x 9 + 1 x 8 = 700 + 90 + 8 = 798 (ii) 1000 x 3 + 100 x 1 + 10 x 5 + 1 x 9 = 3000 + 100 + 50 + 9 = 3159 Q4. Test the divisibility of 46602479 by 11. Sol...

Q1. Two quantities x and y are related by the relation y = 5x + 3. Make a point table for 4 different values of x. Solution The relation is: y = 5x + 3 Taking x = 1, y = 5 x 1 + 3 = 8 Taking x = 2, y = 5 x 2 + 3 = 13 Taking x = 3, y = 5 x 3 + 3 = 18 Taking x = 4, y = 5 x 4 + 3 = 23 Table is: x 1 2 3 4 y 8 13 18 23 Q2. Write X-coordinate and Y-coordinate of the following points: (i) (8, -3) (ii) (4, 1) (iii) (-6, 4) Solution (i) In (8, -3) X-coordinate is 8 Y-coordinate is -3. (ii) In (4, 1) X-coordinate is 4 Y-coordinate is 1. (iii) In (-6, 3) X-coordinate is -6 Y-coordinate is 3. Q3. Which of the following points lie on y-axis? (0, 1), (-1, 0), (7, 0), (0, -4), (0, 4), (5, 0) Solution A point with zero x-coordinate lies on y-axis, i.e., a point of the form (0, b) lies on y-axis. Thus, points lying on y-axis are: (0, 1), (0, -4), (0, 4). Q4. Write the name of quadrant in which the following points lie: (i) (-8, 1) (ii) (-3, -1) (iii) (1,...

Q1. Mass of earth is approximately 5,970,000,000,000,000,000,000,000 kg. Express this mass in standard form. Solution Mass of earth = 5,970,000,000,000,000,000,000,000 kg = 597 x 10000000000000000000000 kg = 597 x 10 22 kg = 5.97 x 10 24 kg Q2. Express the following in usual form: (i) 1.002 x 10 6 (ii) 5.54 x 10 7 Solution (i) 1.002 x 10 6 = 1.002 x 1000000 = 1002000 (ii) 5.54 x 10 7 = 5.54 x 10000000 = 55400000 Q3. Write the following in standard form. (i) 458000 (ii) 1780000 (iii) 85000 Solution (i) 458000 = 4.58 x 100000 = 4.58 x 10 5 . (ii) 1780000 = 1.78 x 1000000 = 1.78 x 10 6 . (iii) 85000 = 8.5 x 10000 = 8.5 x 10 4 . Q4. Compare the following pair of numbers. (i) 2.5 x 10 3 and 3.5 x 10 2 (ii) 2 5 and 5 2 Solution (i) 2.5 x 10 3 and 3.5 x 10 2 Or, 2.5 x 1...

Q1. Find the surface area of cubes with edge (i) 5 cm (ii) 2.9 cm. Solution Surface area of cube = 6(Side) 2 . (i) Surface area of cube with edge 5 cm = 6(5) 2 = 6 x 25 = 150 cm 2 (ii) Surface area of cube with edge 2.9 cm = 6(2.9) 2 = 6 x 8.41 = 50.46 cm 2 Q2. If the area of a rectangle is 243 sq. m and the length is 27 m, what is the breadth of the rectangle? Solution Area of a rectangle is given by: Area = l x b, where l = length b = breadth Here, area is given as 243 m 2 and its length = 27 m Thus, Area = l x b 243 = 27 x b b = 9 Thus, breadth of the rectangle = 9 m Q3. Raju wants to fence the garden in his house which is in the shape of a rectangle having dimensions 25 m x 18 m. Find the cost of fencing at the rate of Rs 200 per metre. Solution The length of the fence required is the perimeter of the rectangular garden. Given ...

Q1. Define monomial, binomial and trinomial and give two examples of each. Solution Monomial: An algebraic expression consisting only one term is called a monomial. Examples: x 2 y, -5xy 2 Binomial: An algebraic expression consisting two terms is called a binomial. Examples: y - 7x 2 , -6 + x 2 Trinomial: An algebraic expression consisting three terms is called a trinomial. Examples: 1 + x + x 2 , -1 + z 2 - z 2 x 2 , 3x + 2y - z Q2. Classify the following as monomial, binomial or trinomial: (i) 2x + 3y (ii) 2x 3 + 3y 2 - 1 (iii) 2xy + 10 (iv) -9x 4 yz Solution (i) 2x + 3y : Binomial (ii) 2x 3 + 3y 2 - 1 : Trinomial (iii) 2xy + 10 : Binomial (iv) -9x 4 yz : Monomial Q3. Write down the terms in the following expression: (i) -2x 2 y + 5xy + y 3 - 7 (ii) -9xy + 5x 2 y - 3 Solution (i) Terms in the expression -2x 2 y + 5xy + y 3 - 7 are: -2x 2 y, 5xy, y 3 , - 7 (ii) Terms in the expression -9xy + 5x 2 y - 3 are: -9xy, 5x 2 y, -3 Q4. Write the numeric...

Q1. In a book fair 27.5% discount is offered on a book of Rs. 500, then find the discount. Solution Q2. A farmer borrows Rs. 7000 from a co-operative society for 2 years at the rate of 12%. How much does he has to pay at the end of two years? Solution Q3. The sales tax rate is 8%. If Rahul bought a new car and paid a sales tax of Rs 1,920, what was the cost of the car before the tax? Solution Let  us say the car costs Rs y.   That would mean that y multiplied by 8% is Rs 1920.  y(8%) = 1920 8% could also be expressed as 0.08 Thus, y(0.08) = 1920 y =Rs 24000 The car costs Rs 24000 without tax. Q4. Convert the following ratios into percentage: 1) 3 : 5 2) 1 : 4 Solution Q5. 15 boys earn Rs. 600 in 4 days, how much will 20 boys earn in 7 days? Solution Q6. Find the marked price of an article which is bought for Rs. 13489 after a discount of 18%. Solution Q7. The catalogu...