A terminating decimal ends after a certain finite number of decinal places, and does not have to be rounded off. An example would be 378 = 0.875

Your selfterminating decimal fractions are: 2/5, 1/25, and 7/8

So how would I form a conjecture of the terminating decimals?

4 answers

Try to factorize the denominators of all those examples and see if you can come up with a conjecture.

Also, have you done rational and irrational numbers?
More examples of other self-terminating decimals for your conjecture:
1/16 = 0.0625
4/250 = 0.016
3/8 = 0.375
17/50 = 0.34
....
Yes, I figured out the rational and irrational numbers. I din't know what conjectures were or how they related.
Factorize the denominators, examine the factors and see if you would discover something.