The sum of five times a number and three in an algebraic expression

Answer 1

sum of five times a Number and three

= 5N + 3

or possibly the author intended to say 5(N+3)

but PEMDAS, arthmetic order of operations would require Multiplication before Addition

so the 5N would be first, then add +3 afterwards, so 5(N+3) looks like a mistake.

PEMDAS stands for Parentheses first, Exponents 2nd, Multiplication 3rd, Division 4th, Addition 5th, Subtraction last

choice of a particular letter is not required. Most people probably would use x instead of N. Letters at the end of the alphabet tend to be for variables, like x, y and z. Letters at the beginning, a, b and c, for constants. But often just use a letter that is the first letter of a word in the problem, such as N for Number, or t for tickets if the problems is about the number of tickets. Odds are 5x+3 would be top choice, but no particular letter is required. Greek letters tend to be for angles.