MATH WORD PROBLEM- PLEASE EXPLAIN STEP BY STEP ?

D*P=243

P=3D

=>

3D^2=243

=>

D^2=81

=>

D=+/-9 (reject -9)

=>

P=27

Phil's age is 27.

D*P = 243

D(3D) = 243

D^2 = 81

D = 9

Phil is 27 years old.

dp = 243;

p=3d;

Therefore d*3d= 243, ie., d^2 = 81, ie., d = 9;

Therefore p = 3*9 = 27.

  The product of the ages of Dora and Phil is 243. 

  Phil is 3 times as old as Dora. 

  How old is Phil?

  DP = 243

  3D^2 = 243

  D^2 = 81

  D = 9

  Phil is 27 years old.

D * P = 243

P = 3D

Solve the system of equations.

D = 9

P = 27

Dx P = 243 

P = 3D 

Substitute 

D x 3D = 243 

3D^2 = 243 

D^2 = 243/3 = 81

D = sqrt(81) = 9 

Hece P = 3x 9 = 27 

You have two unknown variables. Label them. 

You have information about those variables forming two equations. Two unknowns with two equations => you can solve for the unknowns. 

D•P = 243

P = 3D

substitute

D(3D) = 243

3D² = 243

D² = 81

D = √81 = 9

P = 3D = 27

check

27•9 = 243