If you subtract my number from 300, or if you add my number to 220, you will get the same result. What is my number?

40

Step-by-step explanation:

Subtracting a number k from 300 looks like this 300-k.

Adding a number k to 220 looks like this 220+k.

They are saying for some number k that we have 300-k and 220+k is the same value.

That is, 300-k=220+k.

This is the equation we are going to solve for your number.

300-k=220+k

Add k on both sides:

300=220+2k

Subtract 220 on both sides;

80=2k

Divide both sides by 2:

40=k

k=40.

So the number is 40.

Check: 300-40=260 while 220+40=260.