In a triangle, 3/4 of one of the angles is 15 degrees. How many degrees is 1/5 of this angle?

If 15 ° is 3/4, then following from this you can find the whole angle, i.e. its 4/4.
To do this, divide 15 ° by 3/4, or divide by 3 (the number of parts in 15 °) and multiply by 4 (how many parts are in the angle).
We get 15/3 * 4 = 20 ° – this is the full angle.
Now, to find it 1/5, we can simply divide it into 5 parts and get 4 °.