Mixture A is 20% oil and 80% material B by weight. If 2 more kilograms

Question

Mixture A is 20% oil and 80% material B by weight. If 2 more kilograms of oil are added to the 8 kilograms mixture A, how many kilograms of mixture A must be added to make a 70% material B in the new mixture?

A)6
B)7
C)8
D)9
E)10

Can someone please explain the solution to this problem...

A) 6 
B) 7 
C) 8 
D) 9 
E) 10

Zarrolou · Accepted Answer

To the 8 kg of solution A (which has  0.2*8  kg of oil), 2 kg of oil are added, so the resulting percentage of oil is:

\frac{0.2*8+2}{8+2}=\frac{3.6}{10} , the resulting solution is 36% oil (3.6 kg) and 64% B (6.4 B).
The  x  kg of mixture A that must be added to the new mixture, to obtain a 70% of B, is:

\frac{6.4 + 0.8x}{10+x}=0.7 ,  6.4+0.8x=7+0.7x  so  x=6

A

Hope everything is clear

KarishmaB · Answer

Use weighted averages concept discussed here: https://anaprep.com/arithmetic-weighted-averages/ https://anaprep.com/arithmetic-mixtures/ and these videos: https://www.youtube.com/watch?v=_GOAU7moZ2Q https://www.youtube.com/watch?v=VdBl9Hw0HBg Old mix has 20% oil. You add 2 kgs of 100% oil. You get new mix with 30% oil (70% material B). w1/w2 = (100 - 30)/(30 - 20) = 70/10 = 7/1 For every 7 parts of mix A, you have added 1 part of oil. Since you have added 2 kgs oil, mix A must be 7*2 = 14 kgs. You already had 8 kgs of mix A, so extra mix A added must be 14 - 8 = 6 kgs. Answer (A)

PareshGmat · Answer

Oil ................ Material ................. Total

1.6 .................... 6.4 ........................... 8 (Initial Mix)

After adding 2 units oil

3.6 ....................... 6.4 ........................ 10

Say "x" units of Initial mix is added to the new

3.6 ......................  6.4 + \frac{6.4x}{8}  ................. 10+x

Given that material has to be 70% in the new mix; setting up the equation accordingly

\frac{70}{100} (10+x) = 6.4 + \frac{6.4x}{8}

x = 6

Answer = A

rohit8865 · Answer

Can be done with weighted avg method.
if 2 kg more of oil is added to 20% oil of 8 kg mix,then a 10kg of mix will have 3.6kg (or 36%) of oil .
A1=20(initial mix.)
Avg. is what we need..ie 70% of material B means 30% of oil
A2=36(36% of 10 kg mix)
w1/w2=(A2-Avg)/(Avg-A1)
(36-30)/(30-20)
6/10
means for every 10 kg of new mix. we need 6 kg of mix A
Ans A

gracie · Answer

let a=kilograms of mixture a to be added to new mixture
total oil in new mixture will be 1.6+2+.2a=3.6+.2a kilograms
total weight of new mixture will be 8+2+a=10+a kilograms
(3.6+.2a)/(10+a)=.3 
a=6 kilograms

law258 · Answer

0.20(8+x)+2=(10+x)(0.30)
3.6+0.20x=3+0.30x
0.6=0.10x
 x=6

eduardolarrranaga · Answer

hi there, i'm trying to solve this problem via the alligation method, but I'm stuck. Help is much appreciated!

A = 80-70= 10 
B = 0 - 70 = 70
70:10

solution=7???

not sure why I'm getting this wrong.

JeffTargetTestPrep · Answer

Since mixture A is 8 kilograms by weight originally, it has 0.2(8) = 1.6 kilograms of oil and 0.8(8) = 6.4 kilograms of material B. After 2 more kilograms of oil are added, there will be 3.6 kilograms of oil but there will still be 6.4 kilograms of material B. Notice now we will have 10 kilograms of mixture A.

If we let x = the number of kilograms of mixture A to be added, we are adding 0.8x kilograms of material B, thus we have:

(6.4 + 0.8x)/(10 + x) = 0.7

6.4 + 0.8x = 7 + 0.7x

0.1x = 0.6

x = 6

Answer: A

Jamil1992Mehedi · Answer

Let say X Kg to be added,
then, ATQ,
  8 + 2 + x = (1.6 +2 +0.20X) + 0.70( 8+2+X)
>10 + X = 10.6 + 0.90X
> 0.10X = 0.60
> X = 6 Kg  to be added

ishpreetanand · Answer

VeritasPrepKarishma  : How can this question be solved by the allegation method?

KarishmaB · Answer

I have solved it by allegation here: https://gmatclub.com/forum/mixture-a-is ... l#p1588660 The formula depicts the allegation method.

PaolaGRI · Answer

Hi, can somebody explain me why you ad 0.8 x and not simly x? I wrote: 6,4 + x = (10+x)*0,7 Thanks for your help!

adewale223 · Answer

Initial volume of material B

0.8X8 = 6.4

Let y be volume of mixture A added.

6.4 + 0.8y/10 + y = 70/100

64 + 8y = 70 + 7y

y = 6.

Posted from my mobile device

Kinshook · Answer

Given : Mixture A is 20% oil and 80% material B by weight.
Asked: If 2 more kilograms of oil are added to the 8 kilograms mixture A, how many kilograms of mixture A must be added to make a 70% material B in the new mixture?

Mixture A:
Oil = 20%
Material B = 80%

8 kg mixture A
oil = 1.6 kg
Material B = 6.4 kg

After adding 2 kg oil:
Oil = 3.6 kg
Material B = 6.4 kg

Let x kg of mixture A be added.
Oil = 3.6 + .2x
Material B = 6.4 + .8x
Total = 10 + x

(6.4 + .8x)/(10+x) = 70%
6.4 + .8x = 7 + .7x
.1x = .6
x = 6 kg

IMO A

adewale223 · Answer

It is because any volume of mixture A will contain 20% of oil and 80% of material B.

Posted from my mobile device

Apeksha2101 · Answer

I have a question, why are we taking 0.8x?, shouldn't it be 0.64x, since the new mixture has 64% of material B, so additional Mixture A added should have  6.4 + 0.64x as Material B?

Mixture A is 20% oil and 80% material B by weight. If 2 more kilograms

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

Mixture A is 20% oil and 80% material B by weight. If 2 more kilograms

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards