Discount formula: selling price = original price x 10% discount.

Let the purchase price of this commodity be X yuan, and the following questions can be drawn:

( 1+ 10%)X=900×0.9﹣40

1. 1X=770

X=700

The purchase price of this commodity is 700 yuan.

Extended data:

1, original price × (discount10)

For example, the original price of 70 yuan is 30% off, that is, 70×(3÷ 10)=2 1.

For example, 20% discount means: original price × 20% discount.

2. Original price × discount/10

For example, the original price of 40 yuan is 50% off, that is, 40×5/ 10 =20.

3. Original price ×0. discount

For example, the original price 100 yuan, 10% discount, that is:100× 0.1=10.

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