Which of the following is most likely the next step in the series 5a, 10b, 15c, 20d

The given series ⇒ 5a, 10B, 15c, 20D

Each term consists of a number and letter.

It may be divided into (5 , 10 , 15 , 20 , ) and ( a , B , c , D , )

The series of numbers is arithmetic series.

The first term (a) is 5 and the common difference (d) is 5

It has a general equation = a + (n-1)d

So, next step in the series is the fifth term = a + (5-1)d = 5 +(5-1) ×5 = 25 ⇒⇒ (1)

The series of letters is the sequence of letters from a to z but with the sequence is ( capital , small , capital , )

So, next step in the series will be the letter after D in small case

Which is = e ⇒⇒(2)

From (1) and (2)

∴ The next step in the series ( 5a, 10B, 15c, 20D) is ⇒⇒⇒ 25e  

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jbankston is right, use thhe link and you should find the answer.