In a random sample of 400 electrical components,100 are found to be defective.if the hypothesis is that 20% of the components are defective,what is the standard error of the sample proportion

Answer 1

Standard error = √(pq/n)

From your problem:
p = 100/400, q = 1 - p, and n = 400.

Convert all fractions to decimals.

I'll let you take it from here.