If a number is divided by 15 , it leaves a remainder of 7. If thrice the number is divided by 5,then what is the remainder ???

Ans. - 1 why ?

Confusion here =>

N/15 = 15k + 7

Multiplying both side by 9

3N/5 = 5 (27k)+63 ;

3N/5 = 5 K + 3 ;

so remainder should be 3

What to do??