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GMAT prep problem

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Re: GMAT prep problem

by piyush_nitt » Fri Jan 09, 2009 3:10 am
sumatitandon wrote:If each term in the sum of a1+ a2...........+aN is either 7 or 77 and the sum eguals 350 , which of the following could be equal to N

a) 38
b)39
c) 40
d)41
e) 42
equivalent of eqn will be

(7+77+7+77+77.......) = 350

taking 7 common

7(1+11+11+1.....)= 350
1+11+1+11+1 .......= 50

lets say 1 is X times and 11 is y times there fore

eqn reduces to

X+11Y = 50

X = 39 and Y = 1, satisfy above eqn,

39 - 7's
1- 77

therefore IMO C
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by welcome » Fri Jan 09, 2009 3:12 am
350/7 = 50 - (Not in ans)
350-77 = 273/7 = 39.
39+1 =40 - Answer C.
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by mental » Fri Jan 09, 2009 5:02 am
the numbers can be 7 or 77
all the units digits are 7

the sum is 350
that is the units digit is 0

the sum of 7's will give a units digit of 0, if and only if they are in multiples of 10

only 40, in the answers satisfy this requirement
Ans 40: C
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