# Finding percentage decrease in quantity

I need help in basic maths. Here is the problem, The time 8 seconds optimizes (decreases) by 25%. What is the new time? Please help me out with it.

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Subtract one-fourth of eight from eight; what do you get? – Ｊ. M. Oct 29 '11 at 11:32
@J.M.: Is there a formula for this? This example was easy. If I were to calculate $26%$ instead of $25$ then how would I do that? – Ak1to Oct 29 '11 at 11:40
Don't remember a formula; what you need to remember is what's going on! "Decrease" means you subtract; "Decrease by x%" means that you take x% of the starting quantity and then subtract the result of that from the starting quantity. Haven't you bought anything at a discounted price before? – Ｊ. M. Oct 29 '11 at 11:43
$t=(1-\frac{p}{100})t_0$ – pedja Oct 29 '11 at 11:45