let the number be xy4y − x =1......(i)10x+y−(10y+x) =4510x+y−10y−x =45 9x−9y =45......(ii) From (i) x=4y−1, subst in (ii)9(4y−1)−9y =4536y−9−9y =45 27y = 54 y=2 x = 4 × 2−1 =8−1 =7The no. is 72

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