It's been a few years since I've done algebra, and many more since we've been expected to do it without a calculator like the GMAT rules state. Please help me figure out these two problems without the use of a calculator.

Question

1.
__________________
√(16)(20) + (8)(32) = The answer is -4

2.
1
---------
0.75 - 1

The answer is 24

I don't know how to get these answers. Please help. Thank you.

Answer 1

I have a problem getting your answers two. They have probably been interchanged inadvertently.

1.
__________________
√(16)(20) + (8)(32)
=√(64*5+64*4)
=√(64*(5+4))
=8√(9)
=8*3
=24

2.
1
---------
0.75 - 1
=1/(0.75-1)
=1/(-0.25)
=-1/(1/4)
=-4/1
=-4

Answer 2

Thank you, my mistake on mixing up the answers when typing. I get number two now. But on number one, how do you get to
=√(64*5+64*4)

and then do you combine 64s for
=√(64*(5+4))

thank you so much

Answer 3

I break down 16*20 into its prime factors, or 64*5 to find if the other term has similar factors.
I did find a common factor of 64 by changing 8*32 to 4*64.
The rest you know.