xy =36
⇒ xy = 4 x 9,
⇒ x/9 = 4/y

Correct Option: A

xy =36
⇒ xy = 4 x 9,
⇒ x/9 = 4/y
∴ x : 9 = 4 : y

Number of boy = ( 2140 - 1200 ) = 940

Correct Option: B

Number of boy = ( 2140 - 1200 ) = 940
∴ Boys : Girls = 940 : 1200 = 47 : 60

Ratio of Speed = 2 : 3 : 4
Ratio of time taken = (1/2) : (1/3) : (1/4)

Correct Option: D

Ratio of Speed = 2 : 3 : 4
Ratio of time taken = (1/2) : (1/3) : (1/4) = 6 : 4 : 3

Given that, P : Q = 8 : 15, Q : R = 3 : 2
P : Q : R = (8 x 3) : (15 x 3) : (15 x 2)

Correct Option: C

Given that, P : Q = 8 : 15, Q : R = 3 : 2
P : Q : R = (8 x 3) : (15 x 3) : (15 x 2) = 24 : 45 : 30

∴ P : Q : R = 8 : 15 : 10
Here, consequent of first ratio should be equal to the antecedent of second ratio.

Given, P/Q = 8/15, Q/R = 5/8, R/S = 4/5
∴ P/S = (P/Q) x (Q/R) x (R/S)

Correct Option: A

Given, P/Q = 8/15, Q/R = 5/8, R/S = 4/5
∴ P/S = (P/Q) x (Q/R) x (R/S)
⇒ P/S = (8/15) x (5/8) x (4/5) = 4/15
∴ P : S = 4 : 15