ID 783

ID 1010

The typical healthy resting heart rate in adults is 60–80 beats per minute.

If you live 100 years, how many times will your heart beat?

ID 1064

ID 1088

Anna has 9 eggs. She has two empty egg cartons that can hold six eggs each.

How many more eggs does she need to fill the two cartons?

ID 1089

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What is the smallest positive integer that has 12 different positive divisors, including 1 and itself?

ID 2029

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ID 2231

An hour ago, I notched up 78987 kilometers on my odometer.

The number is palindromic, reading the same backwards as forwards.

How fast was I driving during the last hour if the current number on my odometer is also palindromic?

ID 2265

ID 3144

The speed of sound at sea level is 333 meters / second.

If the sound of an explosion comes 30 seconds later, how far from me was the center of the explosion?

ID 3182

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ID 3955

Choose some of the two-digit numbers on the right so that they add up to exactly 100.

How many numbers do you use?

Do not use any number more than once.

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Positive integers and zero are whole numbers.

If N is a whole number, any other whole number can be represented by one of the expressions:

ID 5280

Find two numbers so that their sum, product and the result of division are the same.

What is the largest number?

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ID 5423

The picture "Mental Count" of Russian painter Nikolay Bogdanov-Belsky contains the simple calculation given below.

Which of the following gives the largest result?

Do not use a calculator.

Image source : Wikipedia

ID 5425

Shakuntala Devi was undoubtedly the most brilliant arithmetic mental calculator of all time. In 1977 she mentally calculated the 23^{rd} root of a 201 digit number in a mere 50 seconds. She toured the world showing how she could do calculations faster than they could be entered into and solved by the computers of the day.

The problem for you is much simpler: Evaluate (without using a calculator) the 6^{th} root of the 25 digit number consisting of 1 followed by all zeros.

Author: Leslie Green

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It is demonstrable by direct computer calculation that any even number greater than 5 can be formed as the sum of two odd prime numbers.

Find one of the two primes that sums to 36.

Author: Leslie Green

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What is the result when the largest two-digit number is multiplied by the second smallest three-digit number?

ID 6538

Put four operations signs between the numbers 1, 2, 3, 4, and 5 to make the largest possible result.

What will it be?

Change the order of the numbers (but they must still be separated by an operations sign), use all four signs, and don't use brackets.

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ID 6975

Cross out 5 digits from the number

54321543215432154321

so that the remaining number is as large as possible.

What are the first five digits of the result?

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ID 7193

*Do this in your head. No pen, paper, or calculator.*

Start with something

multiply it by 3

add 1

multiply the result by 4

subtract 1

The result is 15.

What is the something we started with?

ID 7397

I write a 4-digit number on a sheet of paper, then turn the sheet upside down and the value of the number becomes smaller.

If the ratio of the numbers is about 0.8667, what is the original number?