10) 9 stacks of chairs
The question is asking for the amount of chair stacks there will be where no chairs are left lingering.
Divide the total amount of chairs (45) by the amount of chairs a stack holds (5).
(45) / (5) = 9.
11) 80 cars
A half plus a half equals a whole. Since Eddie now only has 40 cars, this is half of what he originally had before splitting the amount with his brother.
Multiply the current amount of cars (40) by (2)
or
divide the current amount of cars (40) by (1/2).
(40) * (2) = 80.
(40) / (1/2) = 80.
12) 25 pairs of socks
This question is straightforward. Pairs are units of 2.
50 socks means that each sock in the bundle is assorted with another sock.
Divide the total amount of socks Dad has for washing (50) by the amount of socks that fit in a pair (2).
(50) / (2) = 25.