Tamarind pulp is a super thick brick of tamarind with seeds (you can also get the brick without seeds). Typically you dissolve this in boiling water and press the resulting stuff through a strainer to eliminate the seeds and any other solid matter. The remainder that goes into the recipe is close to tamarind paste.
I'm not sure what the ratio is of paste to pulp. Much of the volume you get will be from the water you add to the paste.
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