If y varies directly as x, then y = kx where k ≠ 0.
If y varies inversely as x, then y = k/x where k ≠ 0.
If y varies jointly as x and z, then y = kxz where k ≠ 0.
If y is partly constant and partly varies inversely as x, then y = k1 + k2/x where k ≠ 0.
Answer : C
Note that b appears in both ratios. So we make b the same for both ratios.
a : b = 3 : 4 and b : c = 2 : 5 = 4 : 10. Then, a : b : c = 3 : 4 : 10.
Therefore, a2 : c2 = 9 : 100
Answer : E
Since y partly varies inversely as x, y should decrease while x increases.
Since y is partly constant, y should not tend to 0.
Answer : E
Similar steps for different questions asking about change in value.
Answer : B
Actual length = (2 x 500) cm = 1000 cm = 10 m
Actual breath = (3 x 500) cm = 1500 cm = 15m
Actual area = 10 m x 15 m = 150 m2
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