waecmaths question:
If $\{x:2\le x\le 18;x\in integer\}$and 7 + x = 4(mod 9). Find the highest value of x
Option A:
2
Option B:
5
Option C:
15
Option D:
18
waecmaths solution:
$\begin{align} & x=\{2,3,4,5,6,7,8,0,10,11,12,13,14,15,16,17\} \\ & 7+x=4(\bmod 9) \\ & \text{Testing for the possible values for }x \\ & x=15 \\ & 7+15=(2\times 9)+4=4(\bmod 9) \\ & x=15 \\\end{align}$
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