Two circular cylinders of equal volumes have their heights in ratio 1 is to 2 find the ratio of their radii.
Let the radio be r1 and r2. Let the height of 1st cylinder=h Let the height of 2nd cylinder=2h.
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Solution of 1st exercise chapter surface area and volume of class 9 NCERT book
Q.1. A piastic box 1.5 m long. 1.25 m wide and 65 cm deep is to be made. It is to be open at the top. Ignoring the thickness of the plastic sheet, determine : i) The area of the sheet required for making the box. (ii)The cost of sheet for it, if a sheet measuring 1 m cost Rs 20. Sol. Here, length - 1.5 m, Breadth- 1.25 m, Height - 65 cm - 0.65 m. Since the box is open at the top, it has only five faces. (i) So, surface area of the box - Ib + 2(bh + hl) 1.5 x 1.25 m? + 2 (1.25 x 0.65 + 0.65 x 1.5) m^2 = 1.875 + 2 (1.7875) m^2 = (1.875 + 3.575) m2 - 5.45 m^2 Hence, 5.45 m^2of sheet is required Ans. (ii) Cost of 1 m^2of the sheet = Rs 20 . cost of 5.15 m^2 of the sheet = Rs 20 x 5.15 m^2 = Rs 109 Ans. Q.2. The length, hreadth and height of a room are 5 m,3 m and 3m. respectively. Find the cost of white washing the walls of the room and the ceiling at the rate of Rs 37.50 per m^2. Sol. Here, l = 5 m, b = 4 m, h = 3 m Surface area of the walls of the room and the ceilling
Top 5 questions related to Ratio for class 8.
1.If the ratio of chocolates to ice-cream cones in a box is 5:8 and the number of chocolates is 30, find the number of ice-cream cones. Solution : Let the number of chocolates be 5x and the number of ice-cream cones be 8x. 5x = 30 → x = 6. Therefore, number of ice-cream cones in the box = 8*6 = 48. 2.Two numbers are in the ratio 3 : 4. If the sum of numbers is 63, find the numbers. Solution: Sum of the terms of the ratio = 3 + 4 = 7 Sum of numbers = 63 Therefore, first number = 3/7 × 63 = 27 Second number = 4/7 × 63 = 36 Therefore, the two numbers are 27 and 36. 3. If x : y = 1 : 2, find the value of (2x + 3y) : (x + 4y) Solution: x : y = 1 : 2 means x/y = 1/2 Now, (2x + 3y) : (x + 4y) = (2x + 3y)/(x + 4y) [Divide numerator and denominator by y.] = [(2x + 3y)/y]/[(x + 4y)/2] = [2(x/y) + 3]/[(x/y) + 4], put x/y = 1/2 We get = [2 (1/2) + 3)/(1/2 + 4) = (1 + 3)/[(1 + 8)/2] = 4/(9/2) = 4/1 × 2/9 = 8/9 Therefore the value of (2x + 3y) : (x + 4y) = 8 :9. 4. A bag contains $510 in the for
Question from IT foundation. A, B, and C can do a work in 20, 45, and 120 days,respectively. They started the work. A left 10 daysbefore and B left 5 days before the completion ofwork. In how many days is the total work completed?
If N is the total time taken, it means that A worked for (N -10) days, B for (N - 5) days and C for N days. Hence (N - 10) * 1/20 + ( N - 5)*1/45 + N/120 = 1 (N - 10) * 18 + ( N -5)* 8 + 3 N = 360 18 N - 180 + 8N - 40 + 3 N = 360 29N = 580 N = 20
Question from IT foundation. A can do a work in 20 days and B can do in 30 days. both of them start the work together and work for sometime then B leaves if A complete the remaining work in 10 days. find number of days which they worked together?
Work done by A in 1 days=1/20 Work done by A in 10 days=1/20×10 =1/2 Total work done by A and B together=1-1/2=1/2 Work done by A and B together in 1 day=1/20+1/30 =1/12 Time taken by A and B together to do 1/2 part of work=1/2÷1/12 =1/2×12/1 =6 Number of days for which they work together is equal to 6