Question

Grandpa is writing a book. Every morning he starts writing vigorously and fills a lot But post-lunch he goes through all that he's written that far (right from day one) and deletes one-fifth of it. He doesn't write anything more that day. At the end of the day the content of his book is still 20% more than that at the end of the previous day. How much percent new content does Grandpa write in the morning?hour did he go wrong?

Comments

50%?

Answer 1

60%

Answer 2

Morning: Content = $C + k$

Afternoon: Keeps $\frac{4}{5}$ of total

$$C_n = \frac{4}{5}(C + k)$$

End of day content is 20% more than previous day

$$C_n = 1.2C$$
So: 

$$\frac{4}{5}(C + k) = 1.2C$$

$$C + k = 1.5C$$

$$k = 0.5C$$
So new content = $0.5C$ = 50% of previous day's content