Mathematics

# The mean of 20 numbers is 18. If 3 is added to each of the first ten numbers, find the mean of the new set of 20 numbers.

$\frac{x}{20}=18\\ x=360\\\\ \frac{x+3\cdot10}{20}=\frac{x+30}{20}\\ \frac{360+30}{20}=\frac{390}{20}=19.5$