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Home > Maths I > Relationships > Direct variation

Maths I

Direct variation

Finding the variation formula (continued)

Example

The weight of a steel bar, W grams, varies directly as its length, L centimetres.

A dirty glove holding an iron bar.

A 15 cm steel bar weighs 210 grams

Find the formula connecting W and L and use the formula to find the weight of a steel bar 24 cm long.

W \propto L

So W = kL

L = 15 when W = 210

Put these values into W = kL to get:

210 = k \times 15

Therefore k = 210/15 = 14

The required formula is W = 14L

W = 14L and L = 24

Therefore W = 14 \times 24 = 336 grams.

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