Lesson eLearning

A child is counting the days of the month and writes the sequence 1, 4, 7, 10, 13, ... How many terms are there up to and including the number 28?

medium 2 marks Class 1 · Mathematics · Patterns
Answer
10

The correct answer is 10 — Thus there are 10 terms up to 28.

Step-by-step solution

  1. Recognize the sequence is an arithmetic progression with first term 1 and common difference 3.
  2. Use the formula (a_n=a_1+(n-1)d) and set (a_n=28).
  3. Solve (1+(n-1)cdot3=28).
  4. Subtract 1: ((n-1)cdot3=27).
  5. Divide by 3: (n-1=9).
  6. Add 1: (n=10).
  7. Thus there are 10 terms up to 28.
Common mistake: Using an incorrect common difference or misapplying the formula

Concept tested: Finding number of terms in arithmetic series

Published · How this solution was prepared and checked

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