7) C

We first need to calculate what the prices are on Wednesday relative to the prices on other days.

Helen
Helen bought £1000 worth of this share on Monday.
Price on Tuesday = 120% x 1000 = 1.2 x 1000 = £1200

Let price on Wednesday = 1200P

Price on Thursday = 125% (1200P) = 1.25 x 1200P = 1500P

We know Helen made a total profit of £350
So Helen must have sold the shares for £1350.
1500P = 1350
P = 1350 / 1500 = 0.9
So on Wednesday, the price was 90% of the price on Tuesday, i.e. a 10% decrease

Paul
The price of shares on Wednesday bought by Paul would be 90% of £3000
0.9 x 3000 = £2700

Loss = 3000 – 2700 = £300

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