Q4 of 19 Page 59

y varies inversely with x. If y = 30 when x = 12, find

(1) y when x = 15


(2) x when y = 18


Since, y varies inversely with x,


⇒ y ∝


⇒ y = , where k is proportionality constant.


We have, y=30 and x = 12,


⇒ 30 =


⇒ k = 30 × 12


⇒ k = 360


So, y = …….(i)


(1) We have x= 15


By using equation (i), we get


y=


y = 24


(2) We have, y = 18


18 =


⇒ x = = 20


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