In 1 kg mixture of sand and iron

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BTGmoderatorDC: Moderator; Posts: 7187; Joined: Thu Sep 07, 2017 4:43 pm; Followed by:23 members

In 1 kg mixture of sand and iron

by BTGmoderatorDC » Thu Feb 08, 2018 5:29 pm

In 1 kg mixture of sand and iron, 20% is iron. How much sand should be added so that the proportion of iron becomes 10%?

(a) 1kg
(b) 200gms
(c) 270gms
(d) 1.8kg
(e) 4.5kg

I'm confused how to set up the formulas here. Can any experts help?

OA A

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Source: Beat The GMAT — Problem Solving | Thu Feb 08, 2018 5:29 pm

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 » Mon Feb 12, 2018 4:45 pm

lheiannie07 wrote:In 1 kg mixture of sand and iron, 20% is iron. How much sand should be added so that the proportion of iron becomes 10%?

(a) 1kg
(b) 200gms
(c) 270gms
(d) 1.8kg
(e) 4.5kg

We see that 0.2 kg = iron and 0.8 kg = sand. If we let n = the amount of sand added, we can create the equation:

0.2/(1 + n) = 1/10

2 = 1 + n

1 = n

Answer: A

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