quant problem...
Sat, 2009-06-06 15:20
Can anyone solve it???
Q.An old man has Rs.(1! + 2! + ........ + 50!) ,all of which he wants to divide equally (without fractions) among his 'n' children. Then 'n' is equal to.....
a) 5
b) 7
c) 9
d) 11
Fri, 2010-09-24 15:16
#3
Hi....its very
Hi....its very easy....
Listen - !5 = 1*2*3*4*5=120
or (2*5)*1*3*4=120
2*5 always gives 10....and 2*5 come in all expansion after !5
so 2*5 multiplied any number will result 0 in last digit.....so , afterwards !5 in all expantion the last digit would be 0
hence REMAINDER=0 in all expantion after !5
so,
calculate only for !1+!2+!3+!4=33%5=0 (hence ans is 5)
Correct ans
We need to find the number which exactly divides the above series.
For that we use , elimination of choices...
choice a) 5 : We need to check for the reminder of the sum of 1!+2!+3!+4! when divided by 5 but not for other terms because starting from the term 5!+6!+.... all terms will have 5 in the expansion ..
In this case, the reminder comes out to be 3, so this is not the answer.
Similarly, if we check with other options, 11 comes out to be the answer.
@Freek, can u pls check whether this answer is correct or not?