Question
Some lamp posts are placed along a street at equal distances. The distance between the 1st and the 4th lamp post is 21 m. The distance between the 1st and the last lamp post is 70 m. How many lamp posts are there altogether?
4 m

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Some lamp posts are placed along a street at equal distances. The distance between the 1st and the 4th lamp post is 21 m. The distance between the 1st and the last lamp post is 70 m. How many lamp posts are there altogether?