Question

What is the 87th odd positive number?

Answer 1

This an Arithmetic Progression question: (odd number: 1,3,5,7,...)

1st term a₁ = 1
the common difference is d=2
a term of rank n in a AP = a₁ + (n-1)d, where n = rank of the term.

Now let's apply the formula

a₈₇ = a₁ + (87-1).2
a₈₇ = 173