Case Study

Explain the student's mistake and write the correct expression.

Case context: A student translates 'nine less than a number xx' as 9x9 - x.

Question: Explain the student's mistake and write the correct expression.

Sample answer: The student subtracted xx from 99 instead of 99 from xx. The correct expression is x9x - 9.

Key points:

  • The phrase 'less than' means subtracting from the value that comes after it.
  • The starting value is xx, not 99.
  • The correct expression is x9x - 9.

Rubric: Identifies that the subtraction order is reversed and provides the correct expression: x9x - 9.

0

1

Updated 2026-06-13

Contributors are:

Who are from:

Tags

OpenStax

Elementary Algebra @ OpenStax

Ch.3 Math Models - Elementary Algebra @ OpenStax

Algebra

Math

Prealgebra

Recall in Bloom's Taxonomy

Cognitive Psychology

Psychology

Social Science

Empirical Science

Science

OpenStax Psychology (2nd ed.) Textbook