Question

Th mean of 20 numbers is 18. If 3 is added to each of the first tennumbers

Answer 1

Please see the attachment

Answer 2

sum of 20 no.s = 18×20=360
sum of 20 no.s after adding 3 to first 10 no.s =
39
$average = \frac{sum \: of \: numbers}{no \: of \: numbers}$
$average = \frac{390}{20} = 19.5$