A rainstorm increased the amount of water

A rainstorm increased the amount of water stored in State J reservoirs from 124 billion gallons to 138 billion gallons. If the storm increased the amount of water in the reservoirs to 82 percent of total capacity, approximately how many billion gallons of water were the reservoirs short of total capacity prior to the storm?

3 Explanations

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Elias Toulany

Hi,

What I did is round 138 to 140 and 82% to 80%.

Then I found 10% of 140, being 14.
Then I multipliked 14 by 2 to find 20% - being 28.

I took 28 (20%) and added to 140 (~80%) for 168 (100%).

Is this correct?

My numbers are definitly different than yours - but I still got the correct answer 44 at the end.

The odd thing with your route is that 10% of 140 ends up being 17.5 - but my route has 10% of 140 being 14!

Jan 5, 2017 • Comment

Elias Toulany

And I just realized my mistake - I assume 140 was 100% when I took 10% of it...guess I got lucky!

Jan 5, 2017 • Reply

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Kalifa Howard

If we don't approximate initially we get approx 34 so why can't be select the answer D. My question is when do when to approximate first before actually doing the calculations with the values given?

Jan 7, 2016 • Comment

Sam Kinsman, Magoosh Tutor

If we do all of the calculations without approximating, we get an answer of 44.29. Here's how this works:

x = total capacity
x * 0.82 = 138
x = 138/.82
x = 168.29
168.29 - 124 = 44.29

Also, we know we can approximate first whenver the question asks for an approximate answer.

Jan 8, 2016 • Reply

Mohammad Aasim

I find this explanation more useful as it demands lesser paperwork and caters expanded clarity that the video does.

Aug 10, 2017 • Reply

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Mike McGarry, Magoosh Tutor