The alloy contains 80 g of tin, 40 of lead and does not contain impurities.

The alloy contains 80 g of tin, 40 of lead and does not contain impurities. How many percent is the mass of tin from the mass of the alloy.

1) First, we calculate the mass of the alloy:

80 + 40 = 120 grams.

2) Now we find out how many percent the mass of tin is from the mass of the alloy:

120 grams – 100%,

80 grams – x%,

from here we can write that 120: 80 = 100: x.

According to the main property of proportion, the product of its extreme members is equal to the product of the middle members:

120 * x = 80 * 100,

120x = 8000.

Before us is the product of two numbers – 120 and x, equal to 8000. To find an unknown number, you need to divide the product by a known number:

x = 8000: 120,

x = 66.67.

Answer: 66.67%.