Unit 6 · Algebra
Reversed Number Is 72 More — Last Digit?
Lesson 23 of 24
About this lesson
Let the tens digit = A and units digit = B. Reversing gives 10B + A. The difference is 9(B − A). Set that equal to 72, solve for B − A = 8, then find the only valid digit pair.
Chapters
Question
Timothy writes down the number 24. He reverses the digits to make the number 42. He then works out that 42 is 18 more than his starting number, 24.
Nicole writes down a whole number between 10 and 99. She also reverses the digits of her number. She finds that this makes a number that is 72 more than her starting number.
What was the last digit of Nicole's starting number?
Take your Selective prep further
- Sample questions & worked solutions across core Selective topics
- Digital exam simulator with interactive practice sets
- Personalised progress tracking across all your devices
Already have an account? Log in here
No payment required. Compare Selective plans
Give Your Child the Best Chance at Selective Entry
Join NSW families preparing their children for the Selective Schools Placement Test with the most realistic online Selective practice tests available. First tests free—no credit card required.
Claim Your Free Selective Practice Tests