Absolute Values, Oh My!

Algebra Level 3

x = 2010 1 2 3 99 100 \large x=|||\cdots |||2010-1|-2|-3|-\cdots -99|-100|

What is the value of x x ?


The answer is 76.

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2 solutions

Dragan Marković
Apr 26, 2016

Relevant wiki: Absolute Value Problem Solving - Intermediate

1 + 2 + . . . + 62 = 1953 < 2010 2010 1 2 3 62 = 57 1+2+...+62=1953<2010 \implies || \cdots ||2010-1|-2|-3|-\cdots -62|=57

Then

57 63 64 = 57 + 64 63 = 58 ||57-63|-64|=57+64-63=58 and so on (it gets bigger by one each time)

we get: 2010 1 2 3 99 100 = 57 + ( 64 63 ) + + ( 100 99 ) = 57 + 1 + 1 + + 1 = 57 + 19 1 = 76 |||\cdots |||2010-1|-2|-3|-\cdots -99|-100|=57+(64-63)+\cdots +(100-99)=57+1+1+\cdots +1=57+19\cdot1=76

So x = 76 x=76

(note that from 63 to 100 is 38 numbers. since it take 2 of them to make a result 1 there is 19 such results)

i am the 76th solver! by the way

aryan goyat - 5 years ago

nice solution

PARTH GUPTA - 4 years, 2 months ago
Vineet PaHurKar
Apr 28, 2016

Solve the modulus up to 62 @ because 62 is last +ve After that our question makes an ap then solve it

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