Answer:
5
Step-by-step explanation:
If x is the middle number of the 5 consecutive odd numbers, their product is ...
x(x -2)(x +2)(x -4)(x +4) = x(x² -4)(x² -16) = x⁵ -20x³ +64x
The first 3-digit prime is 101, so the product of that with this is ...
101(x⁵ -20x³ +64x) = 101x⁵ -2020x³ +6464x
Since we're only interested in the units digit, we can find the mod 10 value of this to be ...
(x⁵ +4x) mod 10
Possible units digits of x are 1, 3, 5, 7, 9, so possible units digits of this product are ...
x(x⁴ +4) = 1(1⁴ +4) = 5
3(3⁴ +4) = 3(1 +4) = 5 . . . . mod 10
5(5⁴ +4) = 5(5 +4) = 5 . . . . mod 10
7(7⁴ +4) = 7(1 +4) = 5 . . . . mod 10
9(9⁴ +4) = 9(1 +4) = 5 . . . . mod 10
In every case, the units digit of 101z will be 5.
