Of the 2,500 tons of ore mined daily at a quarry, 0.4

BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

This topic has expert replies

Post new topic Post Reply

Previous Topic Next Topic

M7MBA: Moderator; Posts: 2058; Joined: Sun Oct 29, 2017 4:24 am; Thanked: 1 times; Followed by:5 members

Of the 2,500 tons of ore mined daily at a quarry, 0.4

by M7MBA » Sun Feb 18, 2018 4:59 am

Of the 2,500 tons of ore mined daily at a quarry, 0.4 percent results in a certain pure metal. In how many days of mining will the total amount of pure metal produced at the quarry be equal to the daily amount of ore mined?

A 10
B 100
C 250
D 400
E 1,000

The OA is the option C.

What is the equation that I should use here to solve this PS question? Experts, can you give me some help? Thanks in advanced.

Quote

Source: Beat The GMAT — Problem Solving | Sun Feb 18, 2018 4:59 am

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pm; Location: Palo Alto, CA; Thanked: 2867 times; Followed by:511 members; GMAT Score:800

by [email protected] » Sun Feb 18, 2018 10:28 am

Hi M7MBA,

We're told that of the 2,500 tons of ore mined daily at a quarry, 0.4% results in a certain pure metal. We're asked for the number of days of mining that are needed for the total amount of pure metal produced at the quarry to be equal to the daily amount of ore mined. This question can be solved Algebraically; you can also use the 'spread' of the answer choices and a little logic to solve it without doing much math at all.

If you wanted to do the Algebra, you could work through the following steps:

2500(.04) = 10 tons of pure metal mined each day.

To get 2500 tons of pure metal:
2500 = 10X where X is the number of days of mining
2500/10 = X
X = 250 days

From a pattern/logic standpoint though, we know that if 1% of what we mined each day was pure metal, then it would take 100 days for the total pure metal to equal the 2500 tons of mined material from each day. Since we're actually mining 0.4% of pure metal each day - and 0.4% is a little LESS than HALF a percent, then we will need a little MORE than DOUBLE the amount of time to hit that same total. Thus, we're looking for an answer that's a little greater than 200 days - and there's only one answer that matches...

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

Quote

Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 am; Location: New York, NY; Thanked: 39 times; Followed by:22 members

by Jeff@TargetTestPrep » Thu Feb 22, 2018 4:51 pm

M7MBA wrote:Of the 2,500 tons of ore mined daily at a quarry, 0.4 percent results in a certain pure metal. In how many days of mining will the total amount of pure metal produced at the quarry be equal to the daily amount of ore mined?

A 10
B 100
C 250
D 400
E 1,000

Each day 2,500 x 0.4/100 = 25 x 0.4 = 10 tons of pure metal is mined.

So it will take 2500/10 = 250 days to mine 2500 tons of pure metal.

Answer: C

Jeffrey Miller
Head of GMAT Instruction
[email protected]