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Puzzle Details

The local River Trent is 4,100 inches wide, which happens to be a fantastic number.

There is a magnificent, perfectly straight, bridge which spans the river at right angles.

During a recent survey of the area it was found that one seventh of the overall length of the bridge was on one bank of the river, and one eighth of the bridge was on the other bank.

What is the total length of the bridge that spans the River Trent?

We know that 1÷7 + 1÷8 of the total length is on the banks of the river, and 1÷7 + 1÷8 = 15÷56.

So the river width (4,100 inches) is the remaining 41÷56 of the bridge.

Therefore:

41÷56 x length = 4100

So:

length          = 4100 x 56÷41

length          = 5600

As required.

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