# On Monday, the pollen count was 320 grains per cubic meter. On Tuesday, the pollen count was 15% less. What was the pollen count on Tuesday?

Oct 28, 2016

The pollen count on Tuesday was 272 grains per cubic meter.

#### Explanation:

The formula for calculating the percent change is $p = \frac{N - O}{O} \cdot 100$ where $p$ is the percent change, $N$ is the new value and $O$ is the old value. Substituting what we know gives:

$- 15 = \frac{N - 320}{320} \cdot 100$

Solving for $N$ gives:

$- \frac{15}{100} = \frac{N - 320}{320}$

$\frac{- 15 \cdot 320}{100} = N - 320$

$- \frac{4800}{100} = N - 320$

$- 48 = N - 320$

$320 - 48 = N$

$N = 272$