Please help me answer this math question

Question

please help to solve: Phyllis read 4 pages of a storybook on the 1st day, she read 7 pages on the 2nd day, 10 pages on the 3rd day.if it took her 10 days to finish reading the storybook, how many pages were there in the story book

Answer 1

You do not have enough information to answer this question. If it is stated that this is a series, you can see that the number of pages increases arithmetically by 3 each day, starting with 4. The formula for each day is (1 +3N) where N is the day. So on the tenth day, the number of pages is 3x10 +1 or 31 pages.

4,7,10,13,16,19,22,25,28,31

The formula for the sum of an arithmetic series is the sum of the first plus the last, times 1/2 of the number in the series. (The average of a set of numbers which increases steadily, you add the first and last and divide by 2 to get the average number, then multiply by the number of items in the series. For instance, for the digits 1,2,3,4,5 the average is 1+5 divided by 2 = 3 the sum of the digits is (1+5) x (5/2) = 15.

For the problem, the first and last pages is 4 and 31. (4 + 31) x (10/2) = 175