### Instruction: What is the ones digit of $1 \cdot 3 \cdot 5 \cdot 7 \cdot 9 \cdot 11 \cdot 13$?### Response: To find the ones digit of a product, I only need to look at the ones digits of the factors and multiply them.
I can ignore the tens, hundreds, and other digits, since they will not affect the ones digit.
So, the ones digits of the factors are 1, 3, 5, 7, 9, 1, and 3.
I can multiply them in any order, since multiplication is commutative.
I can start with 1, since that does not change the product.
Then I can multiply by 3, and get 3 as the ones digit.
Then I can multiply by 5, and get 5 as the ones digit.
Then I can multiply by 7, and get 5 as the ones digit again, since 5 times 7 is 35.
Then I can multiply by 9, and get 5 as the ones digit again, since 5 times 9 is 45.
Then I can multiply by 1, and get 5 as the ones digit again, since 5 times 1 is 5.
Finally, I can multiply by 3, and get 5 as the ones digit again, since 5 times 3 is 15.
So, the ones digit of the product is 5.