Question

What fraction is equivalent to 1/10 with the denominator as _____/1000

Answer 1

1 X
------=-------
10 1000

Cross multiply
1x 1000 (=1000)
1000/10 (=100)
100

Answer 2

1/10 is equal to 100/1000, as that way, both the numerator and the denominator are multiplied by 100.
This works because the number multiplying the top and bottom are equal, therefore resulting in no net change.