EXERCISE 3.3 MENTAL MATH A. Determine whether the relation between the quantities involved is direct or inverse proportion. 1. The number of workers and the time required to finish an amount of work 2. The number of workers and the amount of work finished 3. The price per kilogram of rice and the number of kilograms that can be bought with p100 4. The number of persons and the amount of food consumption 5. The number of family members and the length of time to consume 1 sack of rice 6. The quality of the goods and the price of these goods 7. The height of a person and his weight 8. The circumference of a circle and its diameter 9. The time elapsed for a car to cover a distance and the speed of the car 10. The amount of interest on a principal amount and the length of time the principal is investedEXERCISE 3.4 MENTAL MATH A. Give the equation for each of the following statements. 1. N varies directly as P and inversely as Q. 2. Y varies jointly as R and T. 3. B is directly proportional to the square of A and inversely proportional to the cube of C. 4. The area of a triangle varies jointly as the base and the height. 5. The time required to dig a ditch of fixed width and depth varies directly as the length of the ditch and inversely as the number of men working on the job. 6. The volume of a circular cone varies jointly as its height and the square of the radius of its base. 7. The pitch of a stretched vibrating string varies directly as the square of the tension and inversely as the length of the string. 8. The pressure of a gas varies jointly as its density and its absolute - temperature. B. Mentally solve for k. 9. 13= k(39) (3) 10. 210 = k(3) (70) 11. 30= k(15) 4 12. 150 = k(5) (30) 13. 72= k ( 22 ) (32 ) 14. 40= k (10) 32