# Doubt from PnC and Number Theory

How to do these kind of problms? Any General Method is there?

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bro, the general method is by selecting the needed factors onlyâ€¦

For A, 2 should not be taken. So, now we choose from the rest of the factors, and the answer will be (1+1)(2+1)(1+1) - 1 = 11

For B, Atleast one 2 must be taken (for it to be even), and 3 must not be takenâ€¦ now choose from the remaining, which gives (2+1)(2+1)(1+1) â€¦ here, no need to subtract 1, as there arent any improper divisorsâ€¦

For C, use those GP formulas, without taking 7.
so, sum will be
(1+2+2^2+2^3)(1+3)(1+5+5^2)

for D, 5 and 2 must be included

All factors must be divisible by 10.

We can represent the sum of factors as:
10(1+2+2^2)(1+3)(1+5)(1+7) (try expanding, and you will get that they are the sum of all such terms.

And the product will give the answer

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Thank You for typing out the. Solution bro

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i havent fully explained C and D, esp Dâ€¦ so if you want, i can fill it out

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Either of C or D u explain. Uske baad to dusra wala ho hi jayega

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Thank You so much bro :))

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