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Algebra Difficulty 1.4 Junior Find the answer Canada

A circular spinner is divided into three sections. An arrow is
attached to the centre of the spinner. The arrow is spun once. The
probability that the arrow stops on the largest section is $50\%$ . The probability it stops on the
next largest section is 1 in 3. The probability it stops on the smallest
section is

Pick one

Solution

A two-digit number has at least one digit that is a 4 if its tens
digit is a 4 or if its ones digit is a 4.

There are 10 two-digit numbers whose tens digit is a 4.

These are $40,41,42,43,44,45,46,47,48$ , and 49.

There are 9 two-digit numbers whose ones digit is a 4.

These are $14,24,34,44,54,64,74,84,94$ , including 44
which was counted in our previous list.

The number of two-digit numbers that have at least one digit that is a 4
is $10+9-1=18$ .

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Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.