## Alligation question

by Sue
(BC, Canada)

Can you please show me how to figure out the answer.
How many grams of coal tar should be added to 925gm of zinc oxide paste to prepare a 6% coal tar ointment?
Thanks

## Comments forAlligation question

 Mar 30, 2011 A little bit more algebra involved... by: Mike C Set up so .06x = coal tar added.Set up so 925 + .06x = Total Weight.Coal tar Added/Total needs to equal 6%.So.06x/(925+.06x)=6/100cross multiply and solve for x.Take x you found and put it into .06x equation.This should give you the amount of coal tar you need to add.To check your answer, plug your x into .06x/(925+.06x) and it will equal .06 .Good luck!

 Dec 23, 2010 Not an alligation problem by: Anonymous This is not an alligation problem, it is a concentration problem--and a very enlightening one at that!

 Oct 18, 2010 Math correction? by: Feintheart I believe the previous answer would only hold true if the final quantity of ointment were exactly 925. However, the question asks us to add tar until the final balance is 6%. This means we will have more than 925g final product.94% of that product will be the zinc oxide. 6% will be the tar.x/925 = .94/.06Now cross multiply, etc. as above.Works out to 59g or so. You need slightly more than 6% of 925g (55.5g) to give the patient their money's worth.The final ointment will weigh 984g, not 980.5g.The previous answer only gives the patient 5.66% coal tar.925 + 55.5 = 980.555.5 / 980.5 = .0566The above answer would be correct if you scooped/dumped out 55.5g of zinc oxide first before displacing its weight with coal tar.

 Sep 14, 2010 answer to this Alligation Problem by: Anonymous you have 6 g in 100 g so you need to find how many g you need in 925 g 6/100 = X/925 cross multiply to get 5550 = 100X 55.5 = X so you will need 55.5g to make 925g of 6% ointment

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