17 – 7 = 10
10 units + 120 = 7 units + 480
1 unit = 120
10 units = 1200 (chocolate cookies after A ate some)
7 units = 840 (strawberry cookies after A ate 3/7 of it)
4/7 ——-> 840
7/7 ——-> 1470 (strawberry cookies at first)
1 – (5/8) = 3/8 ——-> 1470
5/8 ——-> 2450 (chocolate cookies at first)
2450 – 1200 = 1250

Ans : 1250 chocolate cookies.

Thank you for your help!

17 – 7 = 10   This is the number of chocolate cookies left, right.

10 units + 120 = 7 units + 480  So this is because they are an equal number after A bought more cookies. 

But why is 1 unit 120 cookies? Is it because 7 units + 480  will equal 11 units and if you did the same to the 10 units, you will also get 11 units?

Other than that, the others made perfect sense to me. Thank you!

From “the number of strawberry cookies left was 7/17 of the cookies left”, 7 units (strawberry cookies left) + 780 (strawberries bought) . 17 – 7 = 10. 10 units (chocolate cookies left) + 120 (chocolate cookies bought) due to “in the end, there were an equal number of chocolate and strawberry cookies left.”

“Thank you for your help! (You are welcome.)
17 – 7 = 10 This is the number of chocolate cookies left, right. (Yes.)
10 units + 120 = 7 units + 480 So this is because they are an equal number after A bought more cookies. (Yes.)
But why is 1 unit 120 cookies? (How did you arrive at 1 unit instead of 10?) Is it because 7 units + 480 will equal 11 units and if you did the same to the 10 units, you will also get 11 units? (No, as explained above.)
Other than that, the others made perfect sense to me. Thank you!

10p + 120 = 7p + 480

3p = 360

1p = 120

10p = 1200

12u = 7p = 7 × 120 = 840

1u = 70

35u = 2450

Number of chocolate cookies eaten -> 2450 – 1200 = 1250

Thank you for your help!