We have to find the value of the expression you have given:

1/2 - 3/10 + 2/5

make the denominator of all the terms the same, this would involve multiplying the numerator by the same number for all the terms.

=> 1*5/ 2*5 - 3/ 10 + 2*2/2*5

=> 5/10 - 3/10 + 4/10

=> (5 - 3 + 4) / 10

=> 6/10

=> 3/5

**The required value is 1/2 - 3/10 + 2/5 i = 3/5**