At first let the money be (x)
So if she spent half that mean there would remain half of the Money, which 1/2 of x i.e x/2

And then she spent 1/5 of the remaining money,

Remaining money after half has been spent is (x-x/2)
1/5 of the remaining is 1/5 of (x-x/2)

To know the amount she had left, subtract the half that remain after she spent half from 1/5 of it.

X/2 - 1/5(x-x/2)
Recall that the original amount is #1000 substitute 1000 for x

1000/2 - 1/5(1000-1000/2)

500 - 1/5(1000-500)

500 - 1/5(500)
500 - 100

400(d)

1/2 of #1000
1/2*1000=#500

1/5 of #1000
1/5*1000=200

Money spent=500+200
Money spent=#700

Money left=actual money-money spent
Money left=1000-700
Money spent=#300(C)