Respuesta :
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Define x and y :
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Let Natalie's age be x.
Let Fred's age be y.
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Construct equations:
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Add Natalie's age and Fred's age, the result is 39
⇒ x + y = 39
Add Fred's age to 3 times Natalie's age, the result is 65.
⇒ y + 3x = 65
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Solve x and y :
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x + y = 39 -------------- (1)
y + 3x = 65 ------------ (2)
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From Equation (1) :
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x + y = 39
x = 39 - y
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Sub x = 39 - y into equation (2) :
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y + 3x = 65
y + 3(39 - y) = 65
y + 117 - 3y = 65
2y = 52
y = 26
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Sub y = 26 into equation 1 :
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x = 39 - 26
x = 13
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Find their age :
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Natalie = x = 13
Fred = y = 26
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Answer : Natalie is 13 years old and Fred is 26 years old.
-------------------------------------------------------------------------------------------------------
Define x and y :
--------------------------------------------------------
Let Natalie's age be x.
Let Fred's age be y.
--------------------------------------------------------
Construct equations:
--------------------------------------------------------
Add Natalie's age and Fred's age, the result is 39
⇒ x + y = 39
Add Fred's age to 3 times Natalie's age, the result is 65.
⇒ y + 3x = 65
--------------------------------------------------------
Solve x and y :
--------------------------------------------------------
x + y = 39 -------------- (1)
y + 3x = 65 ------------ (2)
--------------------------------------------------------
From Equation (1) :
--------------------------------------------------------
x + y = 39
x = 39 - y
--------------------------------------------------------
Sub x = 39 - y into equation (2) :
--------------------------------------------------------
y + 3x = 65
y + 3(39 - y) = 65
y + 117 - 3y = 65
2y = 52
y = 26
-------------------------------------------------------
Sub y = 26 into equation 1 :
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x = 39 - 26
x = 13
-------------------------------------------------------
Find their age :
-------------------------------------------------------
Natalie = x = 13
Fred = y = 26
---------------------------------------------------------------------------------------------------------
Answer : Natalie is 13 years old and Fred is 26 years old.
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