WAEC 2024 · Paper 1 · Q27

Number bases

The number $1621$ was subtracted from $6244$ in base $x$ . If the result was $4323$ , find $x$ .

Worked solution (try it first)

Check by adding: $4323 + 1621$ must give $6244$ in base $x$ .
Units: $3 + 1 = 4$ , and second column: $2 + 2 = 4$ , with no carries.
Third column: $3 + 6 = 9$ is written as 2 carry 1, so $9 = x + 2$ .
So $x = 7$ , option A.
The last column agrees: $4 + 1 + 1 = 6$ .

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