A book store has twice as many history books as science books. The store has 81 history and science books altogether how many of wach kind does the bookstore have? Write equation too ...

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