Answer:
Below in bold.
Step-by-step explanation:
Let the number of pistachios be x then the number of almonds = x-100.
The number of cashews = 1000 - x - (x - 100) = 1100-2x.
From the info given
3(1100-2x) + 4x + 5(x - 100) = 3700
3300 - 6x + 4x + 5x - 500 = 3700
3x = 3700 - 3300 + 500
3x = 900
x = 300
So there are 300 pistachios, 200 almonds and 500 cashews in the bag.