Spice Kitchen Arithmetic

Algebra Level 3

Harvey has a 2-pound sack of spice mix that contains 6 15 \frac{6}{15} pounds of pepper. The rest of the mix is a combination of cinnamon and cumin. He has a salt-and-pepper mix which consists of 65% pepper and 35 % salt. How many pounds of the salt-and-pepper mix must he add, in order to have a mix that is exactly half pepper?


The answer is 4.

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11 solutions

Alexander Jiang
Feb 4, 2014

We can carefully set up an equation that relates the pounds of pepper to the total pounds of spice mix. We know that the amount of pepper should be half the total amount of spice mix, and we're solving for the amount of salt-and-pepper mix that we should add.

We start with 2 pounds of spice mix that contains 6/15 pounds of pepper. For every p pounds of salt-and-pepper mix we add, we add 0.65p pounds of pepper to the spice mix. So we can write our equation as follows: 6 15 + 0.65 p = 1 2 ( 2 + p ) \frac{6}{15} + 0.65p = \frac{1}{2}(2+p) 6 15 + 13 20 p = 1 + 1 2 p \frac{6}{15} + \frac{13}{20}p = 1+\frac{1}{2}p 3 20 p = 9 15 \frac{3}{20}p = \frac{9}{15} p = 4 \boxed{p = 4}

can someone show me where i went wrong? 2 * 6/15 = 12/15 4/3 * 0.65 = 13/15 2 * (12/15 + 13/15) = 2 + 4/3 = 3.33333333... add 4/3 mix and it works or not?

Will Wombell - 7 years, 4 months ago

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I also calculated this way, but the problem stated that 6/15 pounds of pepper in 2 pound mix. This is not a per pound data :(

Humaid Ashraf - 7 years, 4 months ago

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That makes more sense...

Harshal Sheth - 7 years, 3 months ago

Here's how I did it mentally:

6/15lb of pepper out of 2 pounds is 6/30 = 20% pepper. We are mixing with 65% pepper with a goal of 50%.

65 - 20 = 45 % difference in strength

50 - 20 = 30 % increase needed

Need a 2:1 ratio of strong:weak

This should help for making mixed drinks :)

Ben Resnick - 7 years, 4 months ago

you got it wrong. As there are 6/15 pounds of pepper in the original spice mix, you are taking 6/15th part of 2

Muhammad Zahid - 7 years, 3 months ago

where did you get the 4/3?

Rex Sace - 7 years, 4 months ago

L e t : Let: x = x = mix which consists of 65% pepper and 35 % salt

( 6 15 + 0.65 x ) ( 2 + x ) = 0.5 \frac{(\frac{6}{15} + 0.65x)}{(2 + x)} = 0.5

2 ( 6 15 + 0.65 x ) = ( 2 + x ) 2(\frac{6}{15} + 0.65x) = (2+x)

12 15 + 1.3 x = 2 + x \frac{12}{15} + 1.3x = 2 + x

1.3 x x = 2 12 15 1.3x - x = 2 - \frac{12}{15}

0 , 3 x = 1.2 0,3x = 1.2

x = 1.2 0.3 = 4 \boxed{x =\frac{1.2}{0.3} = 4}

Hello Alimun! I've upvoted ur solution.Plz EDIT it & write 0.3x=1.2 in place of 0,3x=1.2 .

Kaushik Chandra - 4 years, 8 months ago
Aditya Joshi
Feb 10, 2014

Total number of pounds in the sack is 2 2 .

Now, the final condition we want is that half of the bag should be pepper.Thus, new weight of the bag new weight of pepper = 2 1 \dfrac{\text{new weight of the bag}}{\text{new weight of pepper}} = \dfrac{2}{1} .

This just means that the amount of stuff in the bag is twice the amount of pepper.

Let the amount of pounds added to the bag be x x .

Now, 2 + x ( 6 15 + 0.65 x ) = 2 1 \dfrac{2 + x}{\left( \dfrac{6}{15} + 0.65x \right)} = \dfrac{2}{1}

18 15 = 0.3 x \dfrac{18}{15} = 0.3x

The 0.65 x 0.65x is because, for every x x pounds, 65 % 65 \% of it will be pepper.

Thus, solving the equation above to get x x , we find that x = 4 \boxed{ x = 4}

Out of 2-pound sack we have 6/15 pounds of pepper=0.4 pounds

The rest of the mixture consists of 1.6 pounds of (cinnamon and cumin).

Given salt-and-pepper mix has 65% pepper and 35% salt.

Let the no: of pounds of salt-and-pepper mix be x

Then,the no: of pounds of pepper should be equal to the rest of mixture (As we need exactly half pepper)

0.4 + x 0.65 = 1.6 + x 0.35

Solving this we get x=4

Hence,4 pounds of salt-and-pepper mix must be added in order to have a mix that is exactly half pepper.

D K
Feb 22, 2014

Let the no. of required pounds be x. Equation: (65x/100) + (6/15) = (50/100) X (2 + x) Solve it. You will get x= 4 pounds Hurray!

Saleh Elsbahi
Feb 16, 2014

let pounds of the salt-and-pepper mix must he add = X

THEN 6/15 +0.65X = 0.5(2+X)

             X = 4
Nitish Tayal
Feb 12, 2014

Let x be the pounds added. Then, 6/15 + 65x/100 = 1+x/2 9/15 = 15x/100 x = 900/225 or x = 4

Amlan Mishra
Feb 10, 2014

Let the required amount of the salt-and-pepper mix be 'p' pounds.

Then, 6/15 + 0.65p = 1/2 x (2+p)

Solving we get, p = 4

Therefore, 4 pounds of the salt-and-pepper mix he must add, in order to have a mix that is exactly half pepper.

Andy Gudge
Feb 4, 2014

Start with 6/15 pounds pepper out of 2 pounds. Add x pounds of pepper-salt mix. pepper is now 6/15 + 0.65x while total is 2+x, so 0.4 + 0.65x = 0.5(2+x) so 0.4 + 0.65x = 1 + 0.5x so 0.15x = 0.6 so x = 0.6 / 0.15 = 4

Robin Leach
Feb 4, 2014

Let P be the number of pounds of pepper we have, S = the total number of pounds of salt, cinnamon and cumin, T = the total amount we have of everything and X be the number of pounds of the salt and pepper mix we add, and so this is the value we are looking for.

T = 6/15 * P + 24/15 * S + (0.65P + 0.35S)X

T = 0.4P + 1.6S + 0.65PX + 0.35SX

Factorising that we get

T = (0.4 + 0.65X)P + (1.6 + 0.35X)S

We know the ratio of pepper to other spices is 1:1, therefore

0.4 + 0.65X = 1.6 + 0.35X

0.3X = 1.3

X = 4 \boxed{X = 4}

Cant you do (6/15+65x/100)/2+x=1/2 where x is the uknown value of the salt and pepper mass and then simplify.

Jack Abel - 7 years, 4 months ago

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no go home

Robin Leach - 7 years, 4 months ago
Suren Raju
Feb 4, 2014

Let the amount of salt and pepper mix to be added to the 2 pound sack be X pounds. Then the ratio of pepper to the final mixture is (6/15 + 0.65X)/(2+X) ans this must be equal to 1/2. Solving for X, we get X=4 pounds.

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