MATHEMATICS

JAMB 2019 - Question 25

Mathematics 2019 JAMB Past Questions - Question 25: The 4th term of an AP is 13 while the 10th term is 31. Find the 21st term.

The 4th term of an AP is 13 while the 10th term is 31. Find the 21st term.
A:
B:
C:
D:
Examkits App

Examkit's JAMB CBT App

Practice JAMB offline with our Online, PC and Mobile App

  • ✅ 25+ years of past questions (2000 to 2025)
  • ✅ Video solutions and explanation to questions
  • ✅ E-library
  • ✅ Study by topic
  • ✅ And more.

Correct Answer

C

Explanation

To find the 21st term of an arithmetic progression (AP) when the 4th term is 13 and the 10th term is 31, we can use the formula for the nth term of an AP:\[ a_n = a_1 + (n-1)d \]Where:- \( a_n \) is the nth term- \( a_1 \) is the first term- \( n \) is the term number- \( d \) is the common differenceWe are given that the 4th term is 13 and the 10th term is 31. Using these, we can form two equations:\[ a_4 = a_1 + 3d = 13 \]\[ a_{10} = a_1 + 9d = 31 \]Subtracting the first equation from the second gives:\[ 6d = 18 \]\[ d = 3 \]Now that we have the common difference, we can find the first term by substituting \( d = 3 \) into the first equation:\[ a_1 + 3(3) = 13 \]\[ a_1 + 9 = 13 \]\[ a_1 = 4 \]Finally, we can find the 21st term using the formula:\[ a_{21} = 4 + 20(3) = 64 \]So, the 21st term of the AP is 64. Therefore, the answer is C. 64.

Frequently Asked Questions

Examkits is a JAMB CBT practice platform that provides over 20 years of past questions, Post UTME questions, and detailed video solutions to help students prepare for their exams.

You can practice JAMB past questions online, on Android, or on a desktop using the Examkits app. Just register on our website and choose your preferred device.

Yes. Our Android and Windows versions support offline usage. Once downloaded and activated, no internet is required to use most of the features.

Yes, Examkits provides detailed video explanations for all JAMB past questions from 2000 to 2024, helping students understand how to solve each problem.

Examkits offers free practice for some subjects. However, full access requires a one-time affordable activation fee for each version of the app.