A) 47
B) 59
C) 23
D) 35
Correct Answer: A
Solution :
[a] Since two digit number\[=10x+y\] According to question \[\to \,\,y=2x-\,1\] ... (i) When digits are interchanged then new number \[=10y+x\] Then original number \[-\][new number\[-\]original number] =20 \[\to 10x+y-[10y+x-(10x+y)]=20\] \[\to 10x+y-10y-x+10x+y=20\] \[19x-\,8y=20\] \[19x-8\,\,(2x-1)=20\] (Using eq. (i)) \[19x-\,16x+8=20\] \[3x=12\to \] \[x=4\] From (i) \[y=2\times 4-\,1=y=7\] \[\therefore \]Original number \[=10x+y=10\times 4+7=47\]You need to login to perform this action.
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