SAT original mathematics module 1 question 20

We are given 'a = 5√2' and '2a = √(2x)' to find the value of 'x'

Let's solve:
2a = √(2x);

REM a = 5√2

∴2a = 2(5√2) = √(2x);
10√2 = √(2x); raise BS power 2

[10√2]^2 = [√(2x)]^2;
10 × 10 × √2 × √2 = 2x;
100 ×2 = 2x;
200 = 2x; DIV BS 2
200 ÷ 2 = 2x ÷ 2;
100 = x;
the answer, x = 100.

There're no options in this question, but this is how you would answer this question appropriately.

a) shading number 100 of the first column only.
i.e. 100* (where * represent the other boxes that would be blank)
Then you write '100' in the space provided at the top of the column on the first row

b) shading number 100 of the last column only.
i.e. *100 (where * represent the other boxes that would be blank)
Then you write '100' in the space provided at the top of the column on the first row

c) shading zero on the first columns, then number 1 of the second column, followed by teo consecutive zeros in the third and fourth column (note: no decimal point)
i.e. 0100
Then write '0100' in the space provided at the top of the column on the first row

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