An algebra problem by Denisse Chacon

Algebra Level 2

Raul read a book. the first day he read 5 pages and each following day he read two pages more than the previous day. if you've been reading a total of 20 days. How many pages does the book?

480 190 43 270

Denisse Chacon by Denisse Chacon , 26, Mexico

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1 solution

Anindya Mahajan
Jul 10, 2015

It's just an A.P with the first term 'a' being 5, common difference 'd' being 2 and the total no. of terms 'n' being 20. To find the total number of pages of the book, we simply need to just apply the formula for the sum of 'n' terms of an A.P.

No. of pages in the book= n 2 [ 2 a + ( n − 1 ) d ] = 20 2 { ( 2 ∗ 5 ) + [ ( 20 − 1 ) ∗ 2 ] } = 10 [ 10 + ( 19 ∗ 2 ) ] = 10 ( 10 + 38 ) = 10 ∗ 48 = 480 \frac { n }{ 2 } [2a+(n-1)d]\\ =\frac { 20 }{ 2 } \{ (2*5)+[(20-1)*2]\} \\ =10[10+(19*2)]\\ =10(10+38)\\ =10*48\\ =\boxed{480}

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Moderator note:

Simple standard approach.

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