Hi. Can you help me? I thought of a four digit number yesterday but now I forgot it. All I can remember about it is that:

(A) The sum of the four digits equals 25.

(B) The first digit and the fourth digit are the same.

(C) The sum of the two middle digits is equal to three times the first digit.

(D) The third digit is one more than the second digit.

Can you remind me what number I was thinking of and why I probably thought of it yesterday?

Solution: The four digit number is 5785. You can get it by guessing a number for the first digit and then checking if all the statements fit. For example, if we try 5785 that means:

First digit is 5

Second digit is 7

Third digit is 8

Fourth digit is 5

(A) Is true because 5+7+8+5=25

(B) Is true because the first digit is 5 and that equals the fourth digit which is also 5

(C) Is true 8+7=15 and 5*3=15

(D) is true because 8 is one more than 7

So 5785 checks but no other number does. I was thinking about 5785 because it is the new Hebrew year starting with Rosh Hashanah. Shana Tova!

Ari Blinder is a math educator living in Highland Park and the owner of Math for the Masses, an innovative math tutoring and consulting company. He can be reached at [email protected].