Dear Mrs. Chan,

Here I provide some hints which may be helpful to you.

For 1a, you can first rewrite 0.00025 as 25 x 10^-4 and the same for 49000. Then you should be able to simplify the expression. Remember that the square root of 10^-4 is 10^-2.

For 1b, I don't quite understand the expression because there are some lines. Does it represent a fraction?

For 2, I would show you the solution to part (a) as an example. Since 18 = 2x9, /18 = 3x /2 = mn². For the other parts, you just use the same principle. Please note that 2 = m² and 3 = n². For part (c), please remember 0.5 = 1/2.

For 3, you should use the method of "通分母" to simplify the expression.

For 4, you first multiply both sides by x-y to get x+y = y(x-y). Then try to put the terms with x on one side and then factorize. Then you should be able to find x in terms of y.