Answer:
Because 0 at end after decimal has no value.
Explanation:
Given : Tony's calculator correctly shows

To find : Explain why the number of decimal places in the product is not the same as the number of decimal places in the two factors ?
Solution :
3.4 has 1 number in the decimal place
0.5 has 1 number in the decimal place
So, total we have 2 decimal place
i.e.

But in 1.70 the 0 at end after decimal has no value so we write it as 1.7.
that's why the number of decimal places in the product is not the same as the number of decimal places in the two factors.