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

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/.06

Now 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 = 980.5 55.5 / 980.5 = .0566

The 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