SOLUTION: Each number in a list of numbers is 3 more than the number before it. The fifth number in the list is 8. What is the first number?

Question 1204531: Each number in a list of numbers is 3 more than the number before it. The fifth number in the list is 8. What is the first number?
Found 2 solutions by MathLover1, greenestamps:
Answer by MathLover1(20850) (Show Source): You can put this solution on YOUR website!

if each number in a list of numbers is more than the number before it, then common difference between consecutive term is , so we have an arithmetic sequence

-th term formula is:
where is and is common difference
if the fifth number in the list is , we have and

answer: the first number is

and your sequence formula is:

Answer by greenestamps(13200) (Show Source): You can put this solution on YOUR website!

Don't overlook the fact that solving a problem like this informally using logical reasoning and simple arithmetic is good mental exercise and good problem-solving practice.

You are given that the fifth number is 8, and that each number in the list is 3 more than the number before it.

You are asked to find the first number in the list, which is four numbers before the fifth one.

Going BACKWARDS in the list, each number is 3 LESS than the number AFTER it. So to find the first number given that the fifth number is 8, subtract 3 from 8 four times to find the answer.

8-4(3) = 8-12 = -4

ANSWER: -4

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