The HCF and LCM of two numbers are 9 and 90 respectively. If one number is 18, find the other.

 We know that,

HCF x LCM = Product of 2 numbers  - - - - - - - - - - (1)

Here,

HCF = 9

LCM = 90

1st number = 18

2nd number  = Y

Substituting the values given above in the equation (1)

9 x 90 = 18 x Y

810 = 18 x Y

Y = 810 / 18

Y = 45

Therefore the second number is 45