Answer:
84 men
Step-by-step explanation:
The ratio of men to children is ...
men/children = 35%/30% = 7/6
Given the number of children is 72, the number of men is ...
men/children = 7/6 = men/72
men = (7/6)(72) = 84
There are 84 men at the party.
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<em>Additional comment</em>
The fraction of women is 100% -30% -35% = 35%, the same as the number of men. There are 84 women at the party and 240 total people.
It's a factor. This concept is widely used throughout algebra, and you'll probably bump into it through the end of high school and beyond.
A common use is expressing a term in <em>prime factorization</em>, or reducing a number to its most base parts- primes. For example:

Of course, a number like 13 which is already prime is made up of itself and 1. <em>Factors do not have to be primes.</em> 20 is also reducible through combinations of 1, 2, 4, 5, 10, and 20. Prime factorization is just a handy example.
Basically, factors multiply with each other to create other numbers, and numbers can be reduced down to their factors.
36m+25. ehhwienebtbtbrbve
.333 translated to a fraction would be one-third or 1/3