# Problem of the Day: 1/23/13

The speed of light is approximately $2.99 \times10^8$ meters per second. How many seconds will it take for light to travel the $1.49\times10^{11}$ meters from Earth to the Sun?

Solution to yesterday’s problem:

We can use the blanks method to solve this problem. Since we’re concerned with three-digit numbers, let’s set up three blanks:

____ ____ ____

In the first blank, there can be any digit except zero (then it would be a two-digit number). That’s 9 possibilities.

__9__ ____ ____

In the second blank, there can be any digit 0-9.

__9__ __10__ ____

In the third blank, however, there can only be one digit possible. This is because in order for the number to be a palindrome, the first digit and the last digit must be the same.

__9__ __10__ __1__

Multiplying these numbers, we find that there are 90 three-digit palindromes in all.