For his troops' popcorn fundraiser sale, Mike sold caramel corn for $10, buttered microwave popcorn for $8, and lightly buttered popcorn for $7. By the end of the fundraiser, he had sold 400 items and made $3,272. If he sold twice as many lightly buttered microwave popcorn boxes as the buttered popcorn, how many boxes of each type of popcorn did he sell?

x = caramel corn

y = buttered
z = lightly buttered

x + y + z = 400
10x + 8y + 7z = 3272
2z + z + x = 400 <= here since he sold twice as many LB popcorn as buttered, I replaced the LB with 2z.

OK, since we have two of these equal to 400...

2z + z + x = x + y + z
3z = y + z
2z = y
Substitute this in for y.

x + 3z = 400 => 10x + 30y = 4000
10x + 16z + 7z = 3272 => 10z + 23z + 3272

Now subtract these two equations. 7z = 728, z = 104
2(104) = y
y = 208

104 + 208 + x = 400
x = 88

88 caramel popcorn, 208 lightly buttered and 104 buttered.

To solve this problem, let's assign variables to represent the number of each type of popcorn sold.

Let's say:
x = number of buttered microwave popcorn boxes sold
y = number of lightly buttered popcorn boxes sold

We are given the following information:
- Mike sold a total of 400 items, so:
x + y = 400 -- Equation 1

- The cost of selling caramel corn, buttered microwave popcorn, and lightly buttered popcorn was $3,272, so:
10x + 8y + 7(400 - x - y) = 3272 -- Equation 2
(Note: 400 - x - y represents the number of caramel corn boxes sold)

Now, let's solve this system of equations to find the values of x and y.

Let's start by simplifying Equation 2:
10x + 8y + 2800 - 7x - 7y = 3272
3x + y + 2800 = 3272
3x + y = 472 -- Equation 3

Now we have a system of two equations:
x + y = 400 -- Equation 1
3x + y = 472 -- Equation 3

We can solve this system of equations by substitution or elimination. Let's use elimination:

Subtract Equation 1 from Equation 3:
(3x + y) - (x + y) = 472 - 400
2x = 72
x = 36

Now, substitute the value of x in Equation 1 to find y:
36 + y = 400
y = 400 - 36
y = 364

Therefore, Mike sold 36 boxes of buttered microwave popcorn and 364 boxes of lightly buttered popcorn.