Games
Problems
Go Pro!

Coffee Math

Pro Problems > Math > Number and Quantity > Number Theory > Digits
 

Coffee Math

Johann was writing out a math problem when he spilled some coffee on his paper. The result was that some digits were covered up, as shown below.

  ♦7♦
+ ♦♦9
-----
  50♦

If all but one of the hidden areas have the same digit, find all possible values for the sum of the hidden digits

Presentation mode
Problem by Mr. Twitchell

Solution

In order to make it feasible for teachers to use these problems in their classwork, no solutions are publicly visible, so students cannot simply look up the answers. If you would like to view the solutions to these problems, you must have a Virtual Classroom subscription.
Assign this problem
Click here to assign this problem to your students.

Similar Problems

Three Digit Number

I'm thinking of a three-digit number. The sum of its digits is between 15 and 20 exclusive. The product of my first and last digits is 18. I don't have any repeated digits, and my digits are not in either ascending order or descending order. I am a multiple of three, but not of six. What number am I?
 

Rhonda's Zip Code

Rhonda’s zip code has five digits. Two of the digits are the same. One of the digits is three times another digit. Three of the digits are consecutive integers. The zip code starts with a zero. What is the largest possible sum for the digits of Rhonda’s zip code?

Grapes on the Vine

The number of grapes on my grape vine is a three digit number. It is 7 times as much as the number of grapes on the vine last year, and 11 times the number of grapes on the vine the previous year. Next year, if I have twice as many grapes as I do this year, the number of grapes will still be a three digit number, but if I have three times as many grapes, the number of grapes will be a four digit number. If I have 21 times as many grapes, the number of grapes will be a five digit number.

If each jar of grape juice requires 20 grapes, how many full jars of grape juice can I make this year?

Set of Five Digit Numbers

S is the set of five-digit numbers such that the digits are in ascending order, there are no repeated digits, the sum of the first two digits is equal to the third digit, and the sum of the third and fourth digits is equal to the two more than the fifth digit. How many elements are in the set S? (Note that the leading digit cannot be a zero).

Three Digit Difference

Two positive integers, A and B, both have 3 digits. A is bigger than B. A – B is between 300 and 400. What is the value of A - B?

 

Three Digits, sum and product

I'm a three digit number. My first two digits multiply to 12, and my last two digits add to 14. What number am I?

Find the Number

My digits are all odd, and they add to 18. My first digit is four more than my last digit, the product of my digits is between 300 and 315, and I am less than 100,000. If my digits are not in descending order, what numbers could I be?

I Have Three Digits

I am a three digit number, and the following things are true about me:

  1. The product of two of my digits is 8.
  2. The sum of my digits is 13.
  3. My first digit is four times my second digit.

What number am I?

Three Digits with Difference

I’m a three digit number, and the sum of my digits is 13. My first two digits differ by 3, and my last two digits differ by 5. What numbers could I be?

Sum of Digits

Find the sum of all the integers between one and 100 which have 14 as the sum of their digits.

Fill in the blanks, All My Digits, Fiona's Telephone Number, My Three Digits, Two Digit Pattern Matching, Back to Back, Digits in a Multiplication Problem, Palindrome Addition, Three Digit Number, Happy New Year, The Middle Palindrome, Reverse Me, Four Digit Number, Five Digit Number

Featured Resources on This Site

Create Christmas ornaments and more
Print fun mazes in many different shapes

Blogs on This Site

Reviews and book lists - books we love!
The site administrator fields questions from visitors.
Like us on Facebook to get updates about new resources
Home
Pro Membership
About
Privacy