# Question

Raina saves her allowance by putting a note into her money box each week. Each note was either a \$2 note or a \$5 note. Her father also puts in a \$10 note every 30 days. The total amount she collected after 365 days was \$278. How many of the notes were \$5 notes?

No of \$10 notes -> (365/30) 12
Amount -> \$120

\$278 – \$120 -> \$158

Assume all \$2notes,

52 * 2 -> 104

158 – 104 -> 54

54/3 -> 18 (\$5 notes)

There were 18 \$5 notes.

Thanks nicnac, do you know why the last part that you need to divide by 3 which gives you \$18 (\$5 notes)?

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lynn01sg wrote:Thanks nicnac, do you know why the last part that you need to divide by 3 which gives you \$18 (\$5 notes)?

This method is call supposition or make a supposition or assumption . Google the bolded keyword, there are many article and youtube examples.
Once you study it you’ll understand why we use the difference.

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lynn01sg wrote:Thanks nicnac, do you know why the last part that you need to divide by 3 which gives you \$18 (\$5 notes)?

Difference: \$5 – \$2 -> \$3

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