Answer:
5 math books
5 science books
Let’s say math books are a in this equation and science books are b.
50a+80b= 650
a+b= 10
a=10-b
50(10-b) +80b=650
500- 50b + 80b= 650
500+ 30b= 650
30b= 150
b=5
Then go back to the equation a+b=10
b=5
a+ 5= 10
a=5
Double check the math:
Math books: 50*5=250
Science books: 80*5=400
400+250=650
Which is equal to total given in problem.