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# Mental Math - Exponent

Hi,

How can I please calculate (1.25)^5 mentally?

Thanks a lot!

Hi,

How can I please calculate (1.25)^5 mentally?

Thanks a lot!

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Not needed - if you ever see yourself with a problem like this either you have done something wrong or there is a simple way to do it (e.g., Rule of 72)

Not needed - if you ever see yourself with a problem like this either you have done something wrong or there is a simple way to do it (e.g., Rule of 72)

Allen has an excellent approach! The goal of math in casing is not to see if you can multiple super hard numbers together like an engineer. The goal is generally, can you figure out quick-and-dirty approaches to complicated situations, to get to the general answer that matters.

Allen has an excellent approach! The goal of math in casing is not to see if you can multiple super hard numbers together like an engineer. The goal is generally, can you figure out quick-and-dirty approaches to complicated situations, to get to the general answer that matters.

Instead, what I'd focus on is that at a 25% growth rate, you'll double in approximately 3 years (due to rule of 72) and then add the same amount again in the next 2 years approximately (due compound growth). In summary, therefore, you can triple in 5 years, so the answer should be around 3. (In reality, when I calculate electronically, the answer is 3.05)

Does this help?

Instead, what I'd focus on is that at a 25% growth rate, you'll double in approximately 3 years (due to rule of 72) and then add the same amount again in the next 2 years approximately (due compound growth). In summary, therefore, you can triple in 5 years, so the answer should be around 3. (In reality, when I calculate electronically, the answer is 3.05)

Does this help?

Very helpful! It's good to know I don't need to focus on complex calculations — Anonymous A on Nov 23, 2020

Hello! I agree that you do not need to make complex calculations in your head and that your approach to solve difficult problems is more important.
Hope it helps,
All the best
GB

Hello! I agree that you do not need to make complex calculations in your head and that your approach to solve difficult problems is more important.
Hope it helps,
All the best
GB

(edited)

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