Question: A mobile data plan charges 3.2 dollars per gigabyte used and then applies a one-time account credit of 1.40...

1. TRANSLATE the problem information

• Given information:
  • Rate: $3.2 per gigabyte
  • Usage: 2.5 gigabytes
  • Credit: $1.40 (reduces the bill)
• What this tells us: We need to calculate total cost, then subtract the credit

2. INFER the calculation approach

• Strategy: This is a two-step problem
• First calculate the total cost before any credits
• Then subtract the credit amount from that total

3. SIMPLIFY to find cost before credit

• Total cost = Rate × Usage
• Total cost = \(3.2 \times 2.5 = 8.0\) dollars

4. SIMPLIFY to apply the credit

• Final charge = Cost before credit - Credit amount
• Final charge = \(8.0 - 1.40 = 6.60\) dollars

Answer: 6.60 (also acceptable: 6.6 or $6.60)

Why Students Usually Falter on This Problem

Most Common Error Path:

Weak TRANSLATE skill: Misunderstanding what "credit" means in billing context

Students might think a credit is an additional charge rather than a reduction. This leads them to calculate: \(8.0 + 1.40 = 9.40\). Since this is a fill-in response, this error leads to an incorrect numerical answer.

Second Most Common Error:

Poor SIMPLIFY execution: Arithmetic errors with decimal operations

Students might make calculation mistakes like:

• \(3.2 \times 2.5 = 8.5\) (instead of 8.0)
• \(8.0 - 1.40 = 7.40\) (subtraction error)

These computational errors result in incorrect final answers despite understanding the problem correctly.

The Bottom Line:

This problem tests whether students can correctly interpret billing terminology and execute a straightforward two-step calculation with decimals. Success depends on understanding that credits reduce charges and performing accurate decimal arithmetic.