Q).  An initial amount of money deposited in a bank account that earns interest is called the principal. In the table below, P stands for the principal, and I stands for the interest earned by that principal for a period of one year at a particular bank. P is directly proportional to I. Graph the direct proportion relationship between P and I. Use 1 unit on the horizontal axis to represent 1 dollar and 1 unit on the vertical axis to represent $50.

a).  Using the graph, find the interest earned when the principal is $350.
b). Write an equation relating P and I. Then find the principal when the interest earned is $15.

Dear Student,

Please find below the solution to the asked query:

From given information we form our graph , As :

a ) From graph we can see that interest earned when the principal is $ 350 =  7 dollar                        ( Ans )


b ) Given : P is directly proportional to I , So

P $\propto$ I ,

P = k I              --- ( 1) , Here k =  Constant of proportionality

From graph we can see that we earn 1 dollar when principle amount is $ 50 , So we substitute I =  1 and P  = 50 in equation 1 and get :

50 = k ( 1 ) ,

k  = 50  , Substitute that value in equation 1 we get :

P = 50 I                                                                       ( Ans )


When the interest earned is $ 15 , We substitute I  = 15 in above equation and get : 

P = 50 ( 15 ) =  750

Therefore,

The principal when the interest earned is $15 =  $ 750                                             ( Ans )


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