Katie has nine books in her locker, which is three less than the number of books in graces locker. How many books does grace have in her locker?

Question

Katie has nine books in her locker, which is three less than the number of books in graces locker. How many books does grace have in her locker?

Answer 1

Sam, if b = the number of books in Grace's locker,

 

9 = b - 3

 

We need b by itself, so we need to move the 3, which is subtracted. We do the opposite, which is adding, but we have to do it to both sides.

 

9 + 3 = b - 3 + 3

 

Since subtracting 3 and adding 3 is 0, the 3 goes away on the right. We can then flip the equation around.

 

b = 12

 

Hope this helps!