RRB NTPC Maths Questions: 5th April 2020

Q1. The perimeter of a rectangular field is thrice the perimeter of a square field. If one of the sides of the square field is 24 m and breadth of the rectangular field is 48 m then find the area of the rectangular field?

(a) 4276 Sq m                 (b) 5354 Sq m          (c) 3892 Sq m              (d) 4608 Sq m

Ans. - (d) Solution: - here       P of rectangular = 3 x P of square

                                   Or         2(L + 48) = 3 x 4 x 24

                                     So       L = 144 – 48 = 96 m

                                     Area of Rect. = 96 * 48 = 4608 Sq m

Q2.  The radius of the circle is equal to two-fifth of the side of the square. The area of     the circle is 616 sq cm. Find the perimeter of a square?

            (a) 152 cm              (b) 166 cm                     (c) 140 cm              (d) 178 cm

        Ans.-  (c)  Solution :- Here        R = 2/5 * a   ( Let Side of Square = a)

                                And         π * R² = 616

                                 So          R = (616*7 /22)^1/2 = 14 cm

                           Side of Square = a = 14*5/2 = 35 cm

                          Perimeter of Square = 35*4 = 140 cm

                                    

 Q3. If the length of a rectangle is increased by 20% while the breadth of the rectangle is decreased by 10% then find percentage change in area of the rectangle?

         (a) 12 % decreased         (b) 8 % decreased      (c) 12 % increased    (d) 21 % increased

       Ans.- (b)         Solution:- let initial length and breadth of rectangle is L and B

                                So              Area = L*B

                              a/c to Question L’ = 6L/5 and B’ = 9B/10

                                    So Area  = 6L/5 X 9B/10 = 54LB/50

                                     Change in Area = 54LB/50 – LB = 4LB/50

                                     % Change = 4LB/50LB * 100 = 8%

                             

Q4. Find the volume of a cylinder, whose radius is one-fourth of the radius of a circle having an area of 2464 cm2. Height of the cylinder is double of its radius?

    (a) 2156 cm³             (b) 2564 cm³              (c) 2272 cm³                               (d) 2678 cm³

      Ans.- (a)           Solution  Let Radius of Circle be r and Radius of Cylinder be R

                               So π * r² = 2464 Or r = (2464*7/22)^1/2 = 28 cm

                                R = ¼ * 28 = 7 cm

                               And Height = 2R =  14 cm

                               So Volume = 22/7 * 7 * 7 * 14 = 2156 cm³

Q5. The area of a rectangular plot is 432 sq cm. The length is 3 times the breadth. If the cost of fencing the plot is Rs. 8 per cm, then find the total cost to fence the plot?

      (a) Rs. 768             (b) Rs. 716                   (c) Rs. 724                  (d) Rs. 652

Ans. – (a)          Solution:-  Here        L = 3B

                                          And   L * B = 432

                                          Or 3B * B = 432  or B = 12 cm

                                             And L = 3 * 12 = 36 cm

                                   Perimeter = 2*(12 + 36) = 96 cm

                                  Total cost = 8 * 96 = 768 Rs.