Question

In the early months of some year one site added 0.4 million new accounts everyday. At this rate, how many days would be needed to add 20 million new

Answer 1

Lets solve this problem by a technique which we call unitary method.

So,
We have,
$0.4 ~million ~accounts ~are ~added ~in~1~day. \\ \\ \frac{4}{10} ~million ~accounts ~are ~added ~in~1~day \\ \\ \frac{4}{10} * \frac{10}{4} ~million ~accounts ~are ~added ~in~1* \frac{10}{4}~day \\ \\ 1 ~million ~accounts ~are ~added ~in~ \frac{10}{4}~day \\ \\ 20 ~million ~accounts ~are ~added ~in~ \frac{10}{4}*20~day \\ \\ 20 ~million ~accounts ~are ~added ~in~ 50~days$