G : H : I is 5 : 3 : 2

After G gives away 50% of her stamps, she has 2.5 units of stamps left.

To make computations easier, we start the question all over again with G : H : I = 10 : 6 : 4.

After G gives away 50% of her stamps, she has 5 units of stamps left.

H and I receive a total of 5 units of stamps from G. Now H and I have a total of 6 + 4 + 5 = 15 units of stamps.

So at this point of time.
G has 5 units of stamps.
H and I have a total of 15 units of stamps.

I has 40% more stamps than G.
40% of G's 5 units is 2 units.
So I has 7 units of stamps now.
H has 15 - 7 = 8 units of stamps now.

So at this point of time.
G has 5 units of stamps.
H has 8 units of stamps.
I has 7 units of stamps.

Recall that at the start,
G had 10 units of stamps.
H has 6 units of stamps.
I had 4 units of stamps.

Check that the total number of units remains 20 at the end.

(a) I had 4 units of stamps at the start and 7 units of stamps at the end. This is an increase of 3 units of stamps. We express this as a percentage of the initial number of units of stamps.

Percentage increase of stamps = 3 / 4 x 100% = 75%.

(b) At the end, I has 1 unit of stamps fewer than H. This corresponds to 24 stamps.

1 unit --> 24 stamps
6 units --> 6 x 24 = 144

So H had 144 stamps at first.

Use this value of 144 to check the validity of this answer.

1 unit --> 24 stamps
6 units --> 144 stamps
10 units --> 240 stamps
4 units --> 96 stamps

G had 240 stamps at first.
H had 144 stamps at first.
I had 96 stamps at first.

There were 480 stamps at first, but the value remains unchanged at the end.

G has 120 stamps at the end after giving away a total of 120 stamps.

Since I has 40% more stamps than G now, I has 140% x 120 = 168 stamps.

H has 480 - 120 - 168 = 192 stamps now.

Clearly I has 24 stamps fewer than H now/

So the answer of 144 stamps is correct.