For Q7, it depends on how many grams of jam she needs to buy.

By comparing 100g, Brand B is cheaper (even without discount). But it’s different if she’s getting 1200g.

For Brand A, we get 3 bottles (1200 grams) at the cost of 2 bottles ($8.40).

For Brand B, each bottle (300 grams) cost $2.40 after 20% discount (80% of $3 is $2.40). Hence, 4 bottles (1200 grams) would cost: $2.40 x 4 = $9.60. Now, Brand B will be more expensive.

For Q8, the median is 8. Therefore, we know the 3rd number is 8.
__ , __ , 8 , __ , __

Since the mode is 7, it must have appeared twice (or more). Therefore, the first 2 numbers are 7.
7 , 7 , 8 , __ , __

Lastly, the mean is 8.4. This means that the total is:
8.4 x 5 = 42

After taking away the first 3 numbers, the sum of last 2 numbers is:
42-7-7-8 = 20

The last 2 numbers must add up to 20. They should be bigger than 8 and must be 2 different numbers, otherwise the mode can’t be 7 again. The only possible combination is:
9 + 11 = 20

Hence, the answer is:
7 , 7 , 8 , 9 , 11