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The number of porper divisors of 1800 which are also divisible by 10, isA. 18B. 34C. 27D. none of these

Answer» We have `1800=2^(3)xx3^(2)xx5^(2)`
Clearly, the required number of proper divisors in same as the number of ways of selecting at least 2 and at least one 5 out 3 identical `2^(s),2` identical `3^(s)and2` identical `5^(s)`.
`:.` Required number of proper divisors `=3xx(2+1)xx2=18`.


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