Mayra did not have a date on a friday night so she decided to mix solutions that she obtained from her garage. she has 9 liters of a 4% -saline solution that must be mixed with a 10% solution to get a 6% solution. how many liters of the 10% solution are needed?

Let be the number of liters of the 10% solution she needs to use. She'd end up with a 6% solution with a volume of liters. The starting solution contains 0.04*9 = 0.36 liter of salt. Each liter of the 10% solution contributes 0.1 liter of salt, so that

Solve for :

so Mayra needs to add 4.5 liters of the 10% solution.

the largest number of the four options is 1.8 x 10-2

you have it in scientific notation.

1.80 x 10-6   = 0.00000180

1.80 x 10-4   = 0.000180 (bigger, or "less small", than the former one)

so

1.8 x 10-2       = 0.0180. as you see. the "less small", or the biggest one of them all.

as you have negative exponent, it means you are dividing 1.8 by 100 (i.e. moving the dot towards left, two times).

if you had positive exponent for the scientific notation, power of tenths, you would be multiplying times 100 (moving the dot towards right) as below:

1.8 x (10)2 = 180

so. if you have negative exponent in scientific notation, move the dot toward left. if it is positive, toward right as many times the exponent tells you.