Bunuel
On a Saturday night, each of the rooms at a certain motel was rented for either $40 or $60. If 10 of the rooms that were rented for $60 had instead been rented for $40, then the total rent the motel charged for that night would have been reduced by 25 percent. What was the total rent the motel actually charged for that night ?
(A) $600
(B) $800
(C) $1,000
(D) $1,600
(E) $2,400
Although this is a longer way but this is what had hit me when doing the question. Hope this helps some of you

So here it goes,
Let $40 rooms be 'a' in count
Let $60 rooms be 'b' in count
Let total rent be 'c'
Hence from first line of the prompt we can create this equation -
40a + 60 b = c
- (1)Now the second says, we removed 10 rooms from $60 lot and had put it out for $40 slots and rent was reduced by 25%, hence our (1) becomes as follows -
\(40 (a + 10) + 60 (b - 10) = \frac{3}{4}c\)
\(40a + 400 + 60b - 600 = \frac{3}{4}c\)
\(40a + 60b - 200 = \frac{3}{4}c\)
- (2)Using (1) and (2),
\(c - 200 = \frac{3}{4}c\)
\(\frac{1}{4}c = 200\)
c = 800
Hence B.Even though it is a little time consuming but can be used when nothing strikes.