Algebra

Seven years ago, Grogg's dad was 9  times as old as Grogg. Four years ago, Grogg's dad was 5 times as old as Grogg. How old is Grogg's dad currently?    

 

(D – 7)  =  9 • (G – 7)    

 D  =  9G – 63 + 7  =  9G – 56    

 

(D – 4)  =  5 • (G – 4)    

 D  =  5G – 20 + 4  =  5G – 16    

 

9G – 56  =  5G – 16    

4G  =  40                                 ==>>    Grogg's current age is 10    

 

D  =  9G – 56  =  (9)(10) – 56    

 

D  =  90 – 56                            ==>>    Dad's current age is 34    

 

check answer   

(34 – 7)  =?  9 • (10 – 7)    ==>    27 = 27  True    

(34 – 4)  =?  5 • (10 – 4)    ==>    30 = 30  True    

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