Discussion on Kundan/Pandey: Number System
Q79. Two numbers 259 and 3x are added. If 5 is at the unit’s place of the result, then the value of x is
a. 37 b. 61 c. 39 d. Can’t say
Q7. The ten’s digit of 1! + 2! + . . . . . .+ 49! Is _______________
a. 4 b. 3 c. 2 d. 1
(b)
all the factorials above 4 will have 0 as its last digit
adding the last digits of the first 4 factorials we get 3 as its last digit
now you are looking too much into the prob....
sometimes we create prob with the question complicating too many things....
ok..for u..if the question appears in quants section put c as the answer and if it is in the verbal section answer could be (c)
happy..
The ten’s digit of 1! + 2! + . . . . . .+ 49! is
a. 4 b. 3 c. 2 d. 1
1! + 2! + 3! + 4! = 33.
The ten’s digit of 5! is 2 (5! = 4! x 5).
The ten’s digit of 6! is 2 (6! = 5! x 6).
The ten’s digit of 7! is 4 (7! = 6! x 7).
The ten’s digit of 8! is 2 (8! = 7! x 8).
The ten’s digit of 9! is 8 (9! = 8! x 9).
From 10! to 49! have last two digits are 00.
The ten’s digit of 1! + 2! + . . . . . .+ 49! is 1.
2^59 so last digit 8 so for unit digit 5 we have to required 7 last digit 3^39 satisfy
Little Star
n/a
Could you plz tell me how did u get x=4m+3, plz explain
Thanks in advance
n/a
Could you plz tell me how did u get x=4m+3, plz explain
Please read his comment once again!!
last digit of 2^59 is 8
so 3^x shpuld end with 7
So sum of last two digit = 8 + 7 = 15 = 4m + 3
that happens when x = 4m+3
Ans is (c)
last digit of 2^59 is 8
so 3^x shpuld end with 7
that happens when x = 4m+3 , where m is any no.
here 4m +3 can be acqired by 39