Ok, the authors of the book apparently have decided that the only way a fifth grader could solve this question would be to “rename” 4 ¼ as 3 5/4 and subtract ¾. Several fifth graders confronted with this rather easy problem simply did the calculation in their heads without “renaming” the larger number.
However, in today’s math world, you absolutely must “show your work.” Thus, a child with even a modest flair for math is told that solving such a question “in your head” is not permitted. So instead of rewarding a kid who “gets it” without the need to “rename” anything, he must go to the trouble of showing his work for every similar problem.
This results in the child a) questioning the sanity of the system and the teacher and 2) seeing math as drudgery rather than enjoying it. And people wonder why China is surpassing the U.S. in science.
PS: Isn’t the instruction to “rename” the number oddly worded? Why not use the word “convert”?