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Science & Math for K6 - K12 Students

Exercises - XXV , XXVI& XXVII
Exercise-XXV
1. The value of a coin varies directly to the square of its radius when its thickness is constant. The radius of a coin is 1.5'' and its value is \$ 2. What will be the radius of a coin if its value is \$ 5
 Sol:

2. The age of Ramson is 4 times that of his son. 5 years ago Ramson was nine times as old as his son at that time. The present age of Ramson is
 Sol: Let the Ramson age be 4x yrs Ramson's son age be x yrs 4x – 5 = 9(x – 5) 4x – 5 = 9x – 45 40 = 5x x = 8 Ramson's present age = 4x yrs = 4 × 8 = 32

3. In an orchard of the trees are mango trees. If the total number of trees is 840, Find the number of other trees in the orchard
 Sol: Number of trees = 840 Number of mango trees = = 140 Number of other trees = 840 – 140 = 700

4. A fruit seller buys oranges at 5 for \$ 8 and sold at 2 for \$ 5. Find the profit %
 Sol: Cost price of each orange = = \$ 1.60 Selling price of each orange = = \$ 2.50 Profit = \$ 2.50 – \$ 1.60 = \$ 0.90

5. Find the cost price of an article which is sold for \$220 at a loss of 12%
 Sol: If CP is \$ 100 then SP will be \$ 100 – \$ 12 = \$ 88 If CP is \$ 100 SP will be \$ 88 If SP is \$ 220 then the CP will be = \$ 250

6. A Levis store gave a discount of 15% on all garments purchased. What will a customer pay for a phant costing \$ 720
 Sol: Discount = 15 % Price of the phant = \$ 720 Discount = = \$ 108 Price after discount = \$ 720 – \$ 108 = \$ 612

7. By selling 18 chocolates a trader loses the selling price of 2 chocolates. Find his loss %
 Sol: Let SP of 1 chocolate = \$ 1 SP of 18 chocolates = \$ 18 Loss = \$ 2 Cost price = Selling price + loss = \$ 18 + \$ 2 = \$ 20

8. A car takes half of the time taken by a truck to go from P to Q. A truck takes 20 hrs to go for the same journey. What is the speed of the truck if the speed of the car is 120 mph
 Sol: Time taken by car = = 10 hrs Distance covered by car = 120 × 10 = 1200 miles Distance covered by truck = 1200 miles Time taken by the truck = 20 hrs Speed of the truck = = 60 mph

9. 'A' goes 10 miles distance with average speed of 6 mph while rest 20 miles he travels with an average speed of 15 mph. What is the average speed of A ?
 Sol: Time taken to cover 10 miles at 6 mph = Time taken to cover 20 miles at 15 mph = Total time taken to cover 30 miles = = =

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