Word problem please!!

[letrifreemath]

Imagine you are making items, 50 items is a pack. The first pack costs $39, every additional pack costs you that same amount + $1 more.
For example:
1st pack = $39
2nd pack = $40
3rd pack = $41 and so on

another way of thinking, start from 0



I have 2 questions

1) Create a formula to find the total cost of 50 items from any point. For example, what is the total cost of 50 items (1 pack) from the 4550th item to the 4600th item?

2) Create a formula to find the total cost of any amount of pack or items (per 50 items). For example, what is the total cost from the 3150th items to the 5250th items?

Really appreciate for helping

 

[Steven G]

My 1st comment is that you have some numbers listed twice in your table! 50, 100, 150, 200, 250, 300 and 350 are listed under multiple prices. You need to fix that.

50 = 50*1 = $39 + $0
100 = 50*2 = $39 + $1
150 = 50*3 = $39 + $2
200 = 50*4 = $39 + $3
250 = 50*5 = $39 + $4
...
900 = 50*18 = $39 +$?

You will also need to know that 1+ 2 + 3 + 4 + ... + n = n(n+1)/2.

Now try to answer your questions.

 

[tri]

Cost of 1st pack is $39+(1-1).
Cost of 5th pack is $39+(5-1).
Cost of nth pack is quite obvious.
Cost of nth to (n+y)th pack is first subtracted from the second.