Question 170506
x varies directly as the square of s and inversely as t.
x = k[s^2/t]
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How does x change when s is doubled? 
x = k[(2s)^2/t] = 4k[s^2/t]

doubling s quadruples x
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When both s and t are doubled?
x = k[(2s)^2/(2t)]
x = 4ks^2/(2t)
x = 2ks^2/t

doubling s and t doubles x
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Cheers,
Stan H.