In an arithmetic series, the value of the nth term is calculated using the equation,
an = ao + (n - 1)(d)
where an and ao are the nth and the 1st term, respectively. d is the common difference, and n is the number of terms.
In the given, an = 48, a0 = 93, d = -5 and n is unknown. Substituting the known values,
48 = 93 + (n - 1)(-5)
The value of n from the equation is 10. Thus, the answer is the last choice.
If you have 8 yellow balloons for every 12 blue balloons, then if you have 20 balloons in total, 8 out of 20 of those balloons will be yellow. Then you can set up this ratio.
Then, you can use either cross multiplication or multiply the numerator and denominator by the same number to help solve for x. Personally, I prefer cross multiplication.
Finally, solve for x and if you had 100 balloons, you will have 40 yellow balloons.
