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LessonsCatch the Flaw

Lesson 06 · Maths · BODMAS with decimals

Step 1 of 4

Find the wrong step

Lumi inspecting an oxygen tank in an underwater station
Your lessonBODMAS with decimalsStretch

The Deep-Sea Robot Dive

A rescue robot begins a deep-sea dive with 48 litres of oxygen. It works for 6 minutes at 3.5 litres per minute, then receives an 8-litre refill.

Starting oxygen
48 L
Use rate
3.5 L/min for 6 min
Refill
+8 L after the dive

Your question

How many litres are in the tank after the refill?

Lumi’s answer: “The robot finishes with 155 litres.”

1

Step 1 of 4

Find the wrong step

Find where the reasoning first breaks

Start with Step 1 and move downward. Choose the first line that stops making sense.

Later lines may be wrong too. Pick the first mistake.

Lumi’s work

These lines form one solution. Read them from top to bottom.

  1. 1

    Model the story as 48 − 6 × 3.5 + 8.

  2. 2

    Work strictly from left to right: 48 − 6 = 42.

  3. 3

    Then 42 × 3.5 = 147, and 147 + 8 = 155.

  4. 4

    So 155 litres remain.