Here my dude, let me explain it:

87 - 25 has a number with an ugly odd number in it: 7. It's not super intuitive to subtract from things or be subtracted from like a 10 or a 5 is, as 10 and 5 we use to count and such a lot more than we count 7. More people are just more familiar with the other numbers.

So, when we're asked to do 87 - 25, it's a lot faster or most people to sort of remove that 7 from the question and add it back later. The process goes like:

87 - 25 = 80 - 25 = 55

Now we just add that little 7 back in, as most people can add any number faster than they can subtract any number:

55 + 7 = 62

Done! Honestly you could even break it down further and go:

55 + 5 + 2 = 62

It really just depends on how comfortable you are with quick addition. This process can be used for really any size of number, like:

129 - 36 = 130 - 30 = 130 - 35 = 95

Now since we rounded those numbers to make them easier, we tack on what we rounded.

95 - 1 - 1 = 93

As another example, let's go 2431 - 733.

2431 - 733 = 2430 - 730 + (1 - 3) = 1700 + (1 - 3) = 1698

It takes a bit of practice, but by rounding out the end of numbers, where most of the difficulty normally is, and adding them back after, mental math can become pretty easy. Just have to work at it!