What is the smallest whole number that is equal to seven times the sum of its digits?
Think about the maximum number of digits a number can have to still be a plausible solution...
The answer to this math riddle is 21. You probably just guessed to answer this math riddle, which is fine, but you can also work it out algebraically. The two-digit number ab stands for 10a + b since the first digit represents 10s and the second represents units. If 10a + b = 7(a + b), then 10a + b = 7a + 7b, and so 3a = 6b, or, more simply, a = 2b. That is, the second digit must be twice the first. The smallest such number is 21.
How do you make the number 7 even without addition, subtraction, multiplication, or division?
How can you write down eight eights so that they add up to one thousand?
How can you take 2 from 5 and leave 4?
How many sides does a circle have?
How many times can you subtract the number 5 from 25?
When John was six years old he hammered a nail into his favorite tree to mark his height. Ten years later at age sixteen, John returned to see how much higher the nail was. If the tree grew by five centimeters each year, how much higher would the nail be?
I am four times as old as my daughter. In 20 years time I shall be twice as old as her. How old are we now?
What did one math book say to the other math book?
Lily is a lilypad in a small pond. Lilly doubles her size each day, On the 20th day she covers the whole pond. On what day was Lily half the size of the pond?
There is a clothing store in Bartlesville. The owner has devised his own method of pricing items. A vest costs $20, socks cost $25, a tie costs $15 and a blouse costs $30. Using the method, how much would a pair of underwear cost?
What did the triangle say to the circle?
One is to three as three is to five and five is to four and four is the magic number. What is the pattern?
If a boy blows 18 bubbles, Then pops 6 eats 7 and then He pops 5 and blows 1. How many are left?
The ages of a father and son add up to 66. The father's age is the son's age reversed. How old could they be? (3 possible solutions).
What two whole, positive numbers have a one-digit answer when multiplied and a two-digit answer when added?
Pick a number from 1-10, multiply it by 2, add ten, divide it by 2, now subtract the number that you have from the number you picked. What is it?
You want to boil a two-minute egg. If you only have a three-minute timer (hourglass), a four-minute timer, and a five-minute timer, how can you boil the egg for only two minutes?
81 x 9 = 801. What must you do to make the this equation true?
How much will a 38° angle measure when looked at under a microscope that magnifies ten times?
If 1=5, 2=15, 3=215, and 4=3215. What does 5 equal?