Predict the result
Add three fifths and four sevenths.

Set up the model
A common denominator describes equal-size pieces.
Use thirty five, then add the numerators.

Work the example
Twenty one thirty fifths plus twenty thirty fifths is forty one thirty fifths.
The mixed number is one and six thirty fifths.

Check the result
Now subtract one eighth from seven twelfths.
Take eight seconds to think before the answer appears.
[Eight-second silent pause to work; the answer remains hidden.]
With denominator twenty four, the answer is eleven twenty fourths.

Interpret the result
Add or subtract numerators only after the denominators match.