Question

If 5/9 of a tank can be filled in 2 minutes, how many minutes will it take to fill the whole tank ? A) 2.4 minutes B) 2.8 minutes C) 3.2 minutes D) 3.6 minutes

Answer 1

Answer:

D.

Step-by-step explanation:

Set this up as a ratio with #parts of tank on top and #minutes on the bottom and then solve it as a proportion with x being the unknown number of minutes in the second ratio.

$\frac{\frac{5}{9} }{2}=\frac{1}{x}$

Notice the 1 in the numerator of the second ratio.  This is because a whole tank is represented by 9/9 which is the same thing as 1.

Cross multiply to solve for x:

$\frac{5}{9}x=2(1)$

To solve for x we will multiply both sides by 9/5:

$(\frac{9}{5})(\frac{5}{9})x=2(\frac{9}{5})$

9/5 and 5/9 cancel each other out when multiplied leaving simply "x" on the left.  And multiplying on the right:

$x=\frac{18}{5}$

which divides to 3.6 minutes