Question

If a is a natural number then the remainder when (5a + 1) (5a + 3) (5a + 4) is divided by 5,is
a) 0
b) 1
c) 2​

Answer 1

I hope you will like my answers.

Now we shall use trile and error method:

Let a be 1

=((5×1+1)(5×1+3)(5×1+4))÷5

=(6×8×9)÷5

=432÷5

The remainder is 2

Let a be 2

=((5×2+1)(5×2+3)(5×2+4))÷5

=(11×13×14)÷5

=2002÷5

The remainder is 2

Let a be 3

=((5×3+1)(5×3+3)(5×3+4))÷5

=(16×18×19)÷5

=5472÷5

The remainder is 2

So the answer is 2