Can you trust your own brain? Maybe, maybe not. Solve the following questions as quickly as you can:

*A book and a banana together cost $2.90. The book costs $2. How much does the banana cost?**A magazine and a pack of gum cost $1.10. The magazine costs $1 more than the pack of gum. How much does the pack of gum cost?**In a lake, there is a patch of lily pads. Every day, the patch doubles in size. If it takes 48 days for the patch to cover the entire lake, how long would it take for the patch to cover half of the lake?*

Almost everyone will get the first question right (the banana costs $0.90). But when it comes to the second two questions, most people’s brains will take a subconscious shortcut that lands them at the wrong answer. The solution to the second question, for example, is $0.05 (the magazine costs $1.05, making it $1 more than the gum), but when researchers posed a similar question to a sample of Harvard students, arguably one of the brightest available sample groups, more than half got it wrong.

Here’s the kicker: the smarter you are, the more likely your brain is going to mess with you.

Researchers posed the third question to a group of 482 students and found that the smarter students were, as gauged by S.A.T. scores and the Need for Cognition Scale, which, according to an article detailing the study in *The New Yorker*, “measures the tendency for an individual to engage in and enjoy thinking”, the more likely they were to answer the question incorrectly, and the more susceptible they were to other cognitive biases.

Although researchers didn’t have an answer as to why this was the case, Dr. Tomas Chamorro-Premuzic, Hogan’s vice president of research and innovation, said the answer lies not in our intelligence, but in our ability to multitask.

“We make hundreds of decisions and consume thousands of bits of information throughout each day, and our brains are overworked,” he said. “So, they create heuristics – biases and shortcuts – to save bandwidth. If you want to make a better decision, try adopting the 90-10 rule. Devote 10% of your time to 90% of the decisions. The more effectively you do this, the more mental resources you can devote to important matters.”

*Editor’s note: The answer to question number three is 47 days. Most people instinctively divide the total days in half, giving an incorrect answer of 24 days.*