Mrs Sim bought a bag for $140. She paid the cashier in $10 and $5 notes. If there were fifteen notes altogether, how many $10 notes were there? Answer: ___

1. Assume all notes are $5 notes and find the total value

Assume all $15$ notes are $\char36{}5$ notes.
Total value $= 15 \times \char36{}5 = \char36{}75$

2. Find the difference between the actual total and the assumed total

Difference in total value $= \char36{}140 - \char36{}75 = \char36{}65$

3. Find the difference in value between one $10 note and one $5 note

Difference in value per note $= \char36{}10 - \char36{}5 = \char36{}5$

4. Calculate the number of $10 notes

Number of $\char36{}10$ notes $= 65 \div 5 = 13$