Scientific notation is always supposed to be
(a number between 1 and 10) x 10^whatever power.
15. (6 x 10⁻⁵)³
The 'cube' works on everything inside the parentheses ...
the 6 and the 10⁻⁵ .
So this thing is (6)³ x (10⁻⁵)³ .
That's (216) x (10⁻¹⁵) . After cleaning up, it's 2.16 x 10⁻¹³ .
19. 3 ˣ 10⁻² / 8 ˣ 10⁻¹
This mess can be written in a slightly different way,
and it may be clearer to you that way:
(3/8) x (10⁻²/10⁻¹)
The 3/8 is 0.375 .
The second factor is 10⁻¹ .
So we have 0.375 x 10⁻¹ . After cleanup, it's 3.75 x 10⁻² .
20. 4.1 ˣ 10⁻⁴ / 1.28 ˣ 10⁻⁵
Write it like this: (4.1/1.28) x (10⁻⁴/10⁻⁵)
The first part is 4.1/1.28 = 3.203125 .
The second part is (10⁻⁴/10⁻⁵) = 10¹
So it boils down to 3.203125 x 10¹ .
21. 1.91 ˣ 10³ / 5 ˣ 10⁻⁴
Write it like this: (1.91/5) x (10³/10⁻⁴)
First part: 1.91/5 = 0.382
Second part: (10³/10⁻⁴) = 10⁷
Put um together: 0.382 x 10⁷ . After cleanup: 3.82 x 10⁶ .