The first example seemed quite obvious. 55 is a multiple of 11, so it is easiest to convert both fractions to a common denominator - 55. The problem, however, was that the pupils did not notice this fact for both denominators, and thus multiplied them together and then calculated large numbers. The first example after adjusting the pupils looked like this 154/605> 165/605. This procedure is not bad, but it is more time and numerically demanding.
The problem, however, was that the pupils did not notice this fact for both denominators, and thus they multiplied them together and then calculated large numbers.