Iron is 90% of the alloy, the rest is nickel. How many kg of iron and how many kg of nickel is contained in an alloy weighing 51 kg?

Let’s compose and solve the proportion:
51 kg. – 100% (all alloy)
x kg. – 90% (iron)
The proportion is made crosswise:
51 / x = 100/90
After that we take x out of the denominator and solve the proportion.
x = 90 * 51/100 = 45.9 kg – This value is the amount of iron in the alloy
Let’s calculate the percentage of nickel in the alloy:
Let x be an iron alloy, then y a nickel alloy. We know iron alloy = 90%
x + y = 100%
y = 100% -90% = 10%
Let’s solve the proportion:
51 kg. – 100% (all alloy)
kg. – 10% (nickel)
y = 51 * 10/100 = 5.1 kg.
Answer: iron 45.9 kg, nickel 5.1 kg.