What is 375900 rounded to the nearest hundred thousand

Rachel reads 1/5 of the pages of a book plus 12 pages on the first day. on the second day, she reads 1/4 of the remaining pages plus 15 pages. on the third day, she reads 1/3 of the remaining pages plus 18 pages. on the fourth day, she reads the remaining 70 pages. how many total pages are in the book?

What is the missing constant term in the perfect square that starts with x^2 -20x

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?