question number 18
the question is asking how many five digit positive integers, divisible by 9, can be written using only the digits 3 and 6?
what i did: using 9x1,9x2, 9x3, 9x4, 9x5, 9x6, 9x7, 9x8, 9x9
9, 18 ,27, 36, 45, 54 , 63, 72, 81
what i notice was the 9=9, 1+8=9 all the way to 9x9 which is 8+1=9
then i use the five digit numbers like 36363/9 but it didn't work.
after few tries i use 33336 and it work!!!
then i tried 33363, 33633, 36333, 63333, 66663, 66636, 66366, 63666, 36666.
all of them work
so the answer is "d" 10
Wednesday, April 14, 2010
Subscribe to:
Posts (Atom)
