Answer: Incomplete question, please edit.
Step-by-step explanation:
Answer:10/7 and mixed number form is 1 3/7
let h= history books
science books = s
h=2s there are 2 times as many history as science so to get them equal we double the science
h+s=81 there are 81 total history and science books
2s+s=81 substitute 2s for h in the above equation
3s = 81 combine like terms
s = 27
There are 27 science books
h=2s
h=2(27)
h=54
there are 54 history books
Marbles in a bag: 3 green, 4 yellow, 5 blue, 8 pink.
Event A - get a green or yellow marble
Event B - get a pink marble
Events A and B are independent because we draw a marble from a bag with 20 marbles in both cases.

Probability of combined events is