Brain Teaser: Can you find the number that will replace the question mark in this puzzle?

Are you a maths whiz? If so, can you solve this brain teaser without using pen and paper or even a calculator?

An ‘easy’ brain teaser was shared on microblogging platform X, and it sparked a conversation about the correct answer. The teaser challenges people to guess the number that will replace the question mark. Are you a maths whiz? If so, can you solve this one without using pen and paper or even a calculator?

Read| This viral maths brain teaser has started a debate on X. Will you be able to solve it?

Brain Teaser: Can you solve this using mental calculations? (X/@Rainmaker1973)

“Can you solve today’s easy brain teaser?” reads the caption written alongside the brain teaser shared on X handle @Rainmaker1973. The brain teaser shows an array of numbers written horizontally and vertically. All you need is to find the missing number. Do you think you can solve this one?

Take a look at the brain teaser here:

“40 is the answer. Pattern for each row: Number 3 = (square root of Number 1×sqaure root of Number 2),” posted an individual.

Another added, “This one is easy, 40. I knew the second I saw 81. You don’t pick 81 out of the blue with 4 next to it.”

“The answer is 40! As the pattern tells you that the third row is the product of the square root of the first two rows. So: 2 x 9 = 18, 6 x 7 = 42, 8 x 5 = 40,” shared a third.

A fourth commented, “The answer is 10. Any other answer apart from 10 is wrong.”

“Answer is 40. Square root the first two, then multiply the results,” wrote a fifth.

A sixth joined, “Multiply the square roots of the first two columns to get the third column.”