Which is the smallest?
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?
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?
What is the smallest positive integer that has 12 different positive divisors, including 1 and itself?
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?
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?
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.
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:
Find two numbers so that their sum, product and the result of division are the same.
What is the largest number?
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
Shakuntala Devi was undoubtedly the most brilliant arithmetic mental calculator of all time. In 1977 she mentally calculated the 23rd 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 6th root of the 25 digit number consisting of 1 followed by all zeros.
Author: Leslie Green
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
What is the result when the largest two-digit number is multiplied by the second smallest three-digit number?
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.
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?
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?
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?
How many whole numbers between 1 and 1000 do not contain the digit 9?
How many black beads are there?
How many line segments are there?
How many 2-digit integers are there in which the sum of the digits is equal to 11?
How many integers from 1 to 100 can be written as the sum of 3 consecutive positive integers?
What is the largest sum of two integers such that their product is 787?
Choose the answer without using a calculator. 
Estimate the number of Metro stations.
January 1st, 2014 was a Wednesday. 
Use three 5's and any math signs to make 19. 
Calculate.
How many times does the digit 7 appear in the answer to 7654321 x 7 ? 
Which card represents the highest number in hex?