If $^{11} P_{r} = 990$ , find ' $r$ '.

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Solution

From the factorisation, we get:
$^{11} P_{r} = 990$
$∴^{11} P_{r} = 11 \times 10 \times 9$
$∴ r = 3$
Since $n = 11$ we start the division by 11

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