Pages of a magazine are numbered starting from 1. Jack was asked to add up the page numbers, but he included one page twice and got a sum of 130. What was the page number that was included twice?
IPM mega finals 2014 STD VI
Answer:
Sum of pages = N(N + 1)/2
to get an estimate of the value of N
we will take N(N + 1)/2 ~ 130
or N(N + 1) ~ 260
The value of N(N + 1) in actual will be less than 260 as one page was counted twice.
IPM mega finals 2014 STD VI
Answer:
Sum of pages = N(N + 1)/2
to get an estimate of the value of N
we will take N(N + 1)/2 ~ 130
or N(N + 1) ~ 260
The value of N(N + 1) in actual will be less than 260 as one page was counted twice.
Guess: N2 = 152 = 225. This is the nearest value to 260. So, N(N + 1) = 15 x 16 =
240
So, N(N + 1)/2 = 120.
Therefore, the page that was counted twice = 130 -120 = 10
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