Akish deposited $900 into a savings account paying 2% compounded quarterly. Two years later she deposited $400 into the same account. One year after that, she withdrew $200. How much money was in the account at the end of 6 years?

Here is their argument. given the obtuse angle x, we make a quadrilateral abcd with ∠dab = x, and ∠abc = 90◦, and ad = bc. say the perpendicular bisector to dc meets the perpendicular bisector to ab at p. then pa = pb and pc = pd. so the triangles pad and pbc have equal sides and are congruent. thus ∠pad = ∠pbc. but pab is isosceles, hence ∠pab = ∠pba. subtracting, gives x = ∠pad−∠pab = ∠pbc −∠pba = 90◦. this is a preposterous conclusion – just where is the mistake in the "proof" and why does the argument break down there?

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Simplify the expression. -2/5(10+15m-20n)