Fo subtract 62-17, mentally talia subtracted 62-20=42 first what should talia fo to find the difference

Talia did 62 - 20 = 42, instead of 62 - 17

Since she subtracted 20 instead of 17, that means she over subtracted by 3. To get the correct answer she has to add back 3 to her initial answer.

Since she over subtracted.

So she has to add 3, that is 42 + 3 = 45

Hope this explains it.