Question 1156484
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You should know how to set up and solve the problem using formal algebra, as shown by the other tutor.<br>
But solving a problem like this using logical reasoning and mental arithmetic is also good brain exercise.<br>
If the sum of their ages is now 29, then 7 years ago the sum of their ages was 29-(2*7) = 29-14 = 15.<br>
If 7 years ago David was twice the age of John, then with their two ages adding to 15 David was 10 and John was 5.<br>
That was 7 years ago; so now their ages are 17 and 12.<br>