Let 80/y = y/20
Then, y ² = 80 x 20 = 1600
? y = ?1600 = 40.

Let (y/21) x (y/189) = 1
Then , y² = 21 x 189 = 21 x 21 x 9
? y = (21 x 3) = 63 .

On dividing 13601 by 86, we get 29 as remainder
? Required number to be subtracted = 29.

Let 392/?x = 28
Then ?x = 392/28 =14
? x = 14² = 196

First four prime numbers are 2,3,5,7,
Their sum = (2 + 3 + 5 + 7) = 17.

The first prime number is 2.

Let 10/11 = 110/N,
Then, 10N = 11 x 110
? N = (11 x 110) /10 = 121.

Required number is 2 x 4 x 6 = 48.

Let quotient = Q and remainder = R
Then, Divisor = 12 Q =5 R
Now, R = 48
? 12Q = 5 x 48
? Q = 20

Dividend = Divisor x Quotient + Remainder
? dividend = ( 20 x 240 + 48 )
= 4848

Let the number be N
According to the question N x ( N x 3)/4 = 10800
? 3N² / 4 = 10800
? N² = (10800 x 4) / 3= 14400
N = ?14400 = 120