Question

What is the last digit of


`1 * 3 * 5 * 7 * 9 * 11 * 13`

A. 1
B. 3
C. 5
D. 7​

Answer 1

Explanation:

When a number is multiplied by 5, the last digit of the product must be 0 (mod 5).

=> Last digit = 0 or 5.

Since 0 is not an option here, the answer must be 5. (C)

Answer 2

Answer C. 5

Explanation:

Product of Odd and Even Numbers

Any number ending in 5 is necessarily a multiple of 5. For example, 85, 1005, 12345 are all multiple of 5.

Any number ending in 0 is a multiple of 5 and even therefore, is a multiple of 10.

Any integer number multiplied by another number ending in 5 gives one of these possible results:

* A multiple of 5 if the number is odd

* A multiple of 10 if the number is even.

The given product 1*3*5*7*9*11*13 is a multiple of 5 because 5 is one of the factors, and since the rest of the factors are all odd numbers, then the result is a multiple of 5 and has its last digit of 5.

Answer C. 5