We are given the sequence:
5, 10, 20, 40, ?
Let’s break it down step by step.
At first, the numbers might seem random, but if you look closely, there is a very clear pattern forming. The key to solving most number sequences is to check how each number relates to the one before it.
Start from the beginning:
- From 5 to 10 → the number is multiplied by 2
- From 10 to 20 → again, multiplied by 2
- From 20 to 40 → once more, multiplied by 2
So the pattern is consistent:
👉 Each number is double the previous one.
Now apply that same rule to the last number in the sequence:
- 40 × 2 = 80
So the next number is:
👉 80
Why this works
This is called a geometric sequence, where each term is multiplied by a constant value (in this case, 2). These types of patterns are very common in brain teasers because they’re simple but still test whether you can spot consistency.
A quick way to check yourself
If you’re ever unsure, go backward:
- 40 ÷ 2 = 20
- 20 ÷ 2 = 10
- 10 ÷ 2 = 5
Everything lines up perfectly, confirming the pattern.
Final Answer:
👉 80