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mepinoargote
- Junior | Next Rank: 30 Posts
- Posts: 21
- Joined: Wed Apr 28, 2010 12:11 pm
OG 182: If the two-digit integers M and N are positive and have the same digits, but in reverse order, which of the following CANNOT be the sum of M and N?
a)181
b)165
c)121
d)99
E)44
M=10t+u and N=10u+t
M+N=11t+11u= 11(t+u)
Must be a multiple of 11, only A is not and thus cannot be the sum of M and N
I don´t understand the official guide explanation, i mean the algebra is pretty simple and makes sense, but how does it come up with the two equations M=10t+u and N= 10 u +t where t and u are 2 digits. Is that a standard rule in this type of questions?
a)181
b)165
c)121
d)99
E)44
M=10t+u and N=10u+t
M+N=11t+11u= 11(t+u)
Must be a multiple of 11, only A is not and thus cannot be the sum of M and N
I don´t understand the official guide explanation, i mean the algebra is pretty simple and makes sense, but how does it come up with the two equations M=10t+u and N= 10 u +t where t and u are 2 digits. Is that a standard rule in this type of questions?
