Question 1139896
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The solution by the other tutor is a fine formal algebraic solution.<br>
You can also get some good practice in logical reasoning by solving the problem informally.<br>
The difference in their ages is 5 years now; it will always be 5 years.
Since the difference in their ages will always be 5 years, Kyle will be twice as old as Bob when Kyle is 10 and Bob is 5.
Since it is 4 years from now that Kyle will be twice as old as Bob, Kyle's age now is 10-4 = 6.