Sagot :
Present ages:
Margaret = x
Kevin = x + 4
Ages next year (+1):
Margaret = x + 1
Kevin = x + 4+1 ⇒ x + 5
Equation:
x + 5 = 2(x + 1)
x + 5 = 2x + 2
x - 2x = 2 - 5
-x = -3
-1(-x = -3) -1
x = 3
Substitute 3 to x:
Present ages:
Margaret = x ⇒ 3 years old
Kevin = x + 4 ⇒ 3 + 4 = 7 years old
ANSWER: Kevin is 7 years old.
Check their ages next year:
Margaret: 3 + 1 = 4 years old
Kevin: 7 + 1 = 8 years old
Next year, Kevin will be 2 times as old as Margaret:
8 = 2 (4)
8 = 8 True
Margaret = x
Kevin = x + 4
Ages next year (+1):
Margaret = x + 1
Kevin = x + 4+1 ⇒ x + 5
Equation:
x + 5 = 2(x + 1)
x + 5 = 2x + 2
x - 2x = 2 - 5
-x = -3
-1(-x = -3) -1
x = 3
Substitute 3 to x:
Present ages:
Margaret = x ⇒ 3 years old
Kevin = x + 4 ⇒ 3 + 4 = 7 years old
ANSWER: Kevin is 7 years old.
Check their ages next year:
Margaret: 3 + 1 = 4 years old
Kevin: 7 + 1 = 8 years old
Next year, Kevin will be 2 times as old as Margaret:
8 = 2 (4)
8 = 8 True
Let x = Margaret's age (present)
x + 4 = Kevin's age (present)
Therefore..
x + 1 = Margaret's age (next year)
x + 4 + 1 = x + 5 = Kevin's age (next year)
2(x + 1) = x + 5
2x + 2 = x + 5
2x - x = 5 - 2
x = 3 - Margaret's age (present)
x + 4 = 3 + 4 = 7 - Kevin's age (present)
Answer: 7 yrs. old
x + 4 = Kevin's age (present)
Therefore..
x + 1 = Margaret's age (next year)
x + 4 + 1 = x + 5 = Kevin's age (next year)
2(x + 1) = x + 5
2x + 2 = x + 5
2x - x = 5 - 2
x = 3 - Margaret's age (present)
x + 4 = 3 + 4 = 7 - Kevin's age (present)
Answer: 7 yrs. old