Brain Teasers Optical Illusions Puzzle Hunts Codes & Ciphers Mechanical Puzzles
Personal Links
Browse Teasers
Search Teasers

Find the Sum

Math brain teasers require computations to solve.


Puzzle ID:#39976
Fun:*** (2.1)
Difficulty:*** (2.61)
Submitted By:shenqiangAcn****!!




Find the sum of all prime numbers between 1 and 100 that are simultaneously 1 greater than a multiple of 4 and 1 less than a multiple of 5.

Open Calculator


Numbers that are 1 greater than a multiple of 4 are 5, 9, 13, 17, 21... where 9 is 1 less than a multiple of 5. lcm(4, 5)=20, therefore the pattern repeats in each 20 numbers.

9 (composite) 29 (prime) 49 (composite) 69 (composite) 89 (prime)

Therefore, the sum of all such numbers is 29+89=118.


What Next?


See another brain teaser just like this one...

Or, just get a random brain teaser

If you become a registered user you can vote on this brain teaser, keep track of
which ones you have seen, and even make your own.



Back to Top

Online Now
9 users and 673 guests

Users In Chat
Follow Braingle!
Tap into all 20,000+ of our brain teasers, riddles and puzzles on your iPhone or iPad.

Braingle in the iTunes App Store
Copyright © 1999-2017 | FAQ | Widgets | Links | Green | Subscribe | Contact | Privacy | Conditions | Advertise | Braingle Time: 11:03 am
Sign In Create a free account