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Two wires that are made up of two different materials whose specific resistances are in the ratio 2 : 3 , length 3 : 4 and area 4 : 5 . If the ratio of their resistance is a b , then what is the value of a + b , where a and b are the smallest positive integers.?

Correct answer

13

Step-by-step solution

Use   R = ρ   l A ∴   R 1 R 2 = ρ 1 l 1 A 1 ρ 2 l 2 A 2 ⇒ R 1 R 2 =   5 8

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