Unit 2 · Number Theory

Cards 4, 2, 9 — Biggest Minus Smallest?

Lesson 4 of 15

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About this lesson

Jo has three digit cards: 4, 2, and 9. She arranges all three to make different three-digit numbers. The question asks for the gap between the biggest number she can make and the smallest. The trap: option C (675) appears if you accidentally use 924 as the largest instead of 942.

Chapters

0:00Introduction
0:23The Question
1:03Formulating the largest three-digit combination
1:36Formulating the smallest three-digit combination
2:04Executing the column subtraction and borrowing
2:46Exam strategy — the symmetric inverse identity
3:53Confirming the final option

Question

Jo has three cards. Each card has a different number on it: 4, 2, and 9.

She uses all three cards to make different three-digit numbers.

What is the difference between the largest three-digit number Jo can make, and the smallest three-digit number Jo can make?

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