Back to Back

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

Back to Back

X is a three-digit number. Y is the number obtained when the digits of X are reversed. Z is the six-digit number obtained by writing X and Y back to back, with X written first. W is the six-digit number obtained by writing Y and X back to back, with Y written first. What is the largest number which the sum of Z and W must be divisible by?

Presentation mode

Problem by allie

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 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?

All My Digits

All my digits are non-zero perfect squares. If you treat my first two digits as a two-digit number, and treat my last two digits as a two-digit number, the sum of these two numbers is also a perfect square. If I am a three digit number, what numbers could I be?

The Middle Palindrome

If all the palindromes between 100 and 1000 were listed in order from smallest to largest, what is the average of the two numbers in the middle of the list?

NOTE: A palidrome is a number which reads the same forward and backward. For example, if you reverse the digits of 97279, you still have 97279.

Three Digit Number

I am thinking of a three-digit number. The sum of my digits is 17. Two of my digits add to 10, and two of my digits are the same. Find all possible values for my number.

Five Digit Number

The sum of the digits of a three digit number is eighteen. The first digit is three more than the last digit. There is a repeated digit in the number. What are all possible values of the number?

Reverse Me

I'm a three digit number. Reverse my digits and subtract, and the result is 198. Reverse my digits and add, and the result is 1272.

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?

Two Digit Pattern Matching

How many two-digit numbers are there such that the digits match at least one of the following patterns:

The digits are both multiples of three.
Neither of the digits are multiples of two.
The digits add to 8.
The digits are perfect squares.

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).

I Have Three Digits

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

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

What number am I?

Three Digits with Difference, Four Digit Number, Coffee Math, Three Digits, sum and product, Palindrome Addition, Digits in a Multiplication Problem, Fill in the blanks, Rhonda's Zip Code, My Three Digits, Sum of Digits, Three Digit Number, Fiona's Telephone Number, Happy New Year, Grapes on the Vine

Blogs on This Site

Book Scrounger

Reviews and book lists - books we love!

Ask Professor Puzzler

The site administrator fields questions from visitors.

Like us on Facebook to get updates about new resources