Tom and Devin have been teaching for a total of 70 years. Devin has been teaching for 5 less than half the number of years that Tom has. How many years has Tom been teaching?
Think hard. Detailed solution:
50
Let x be the number of years Tom has been teaching.

Devin has been teaching for (1 / 2)x - 5 years.

70 = x + ((1 / 2)x - 5).

70 = (3 / 2)x - 5.

75 = (3 / 2)x.

x = 50.

Tom has been teaching for 50 years.

.

Thus, the answer is 50