When I multiply by 4, add 12, divide by 2, then square root, I get 10. What number did I start with?

22

Step-by-step explanation:

To begin, the most reasonable way of figuring out the answer is creating an equation.

In that case, we can represent all possible numbers with the variable "N"

We basically have that 4n + 12 divided by 2 = 100 (because 10^2 = 100)

Simplifying:

4n + 12 : 6 = 100

Multiplying each side by 6:

24n + 72 = 600

Subtracting 72:

528

Dividing by 24:

N = 22

Check:

22 * 4 = 88. 88 + 12 = 100. Square rooting gives 10. Thus, an answer that the number you started with was 22 is correct.