[philonossis]

"Calculate the following percents, expressing each percent to three significant figures"

(a) percent of the elements that are naturally occurring.

(c) percent of the elements that have been dicsovered during the 1900's.

The book states: "Today's total of 115 elements was reached in 1999.
.
Any increase in the number of known elements from 115 will result from the production of additional synthetic elements.  Current theory ... suggests that all naturally occurring elements have been identified.  The isolation of the last of the naturally occurring elements, rhenium, occurred in 1925.
.
Eighty-eight of the 115 elements occur naturally, and the remaining 27 have been synthesized in the laboratory by bombarding samples of naturally occurring elements with small particles."

88 = 76.5% according to my calculator.
The book says 78.6%.

(c) my calculation from information in the book is that 32 elements have been discovered from 1900 through 1999. My calculator says 32 = 27.8% of 115.

The book says 24.7% of elements were discovered in the 1900's.

Can anyone point out a mistake I am making here?

[AWK]

Errors in books also happen.