Express the series using sigma notation. 6 + 9 + 12 + 15. a b c d

Option (d) is correct.

6 + 9 + 12 +15 =

Step-by-step explanation:

Consider the given series expansion 6 + 9 + 12 +15.

since we have to write in series form of 3.

We first write each term of given series in term of 3k or 3k+3

6 can be written as 3(2) or 3(1)+3

9 can be written as 3(3) or 3(2)+3

12 can be written as 3(4) or 3(3)+3

15 can be written as 3(5) or 3(4)+3

Thus, we can write the given series as ,

or  

Since, we have options to choose.

From the given option (d) matches our result.

So,  6 + 9 + 12 +15 =

9 sandwiches per hour

step-by-step explanation:

when we have a rate, we want a 1 in the denominator

27/3 = 9

27 sandwiches/ 3 hours = 9 sandwiches/hour