Rubidium-87 has a half-life of 48.1 billion years. after how many years is there 25 percent parent isotope and 75 percent daughter isotope contained in the object?

96.2 billion years.

Explanation: Half life of Rubidium-87 = 48.1 billion years

Half life is the time required to decay half of the radioactive material. Thus if 100 g of sample is present, 50 g of sample remains after half life and 50 g decays.

For 25 percent parent isotope and 75 percent daughter to remain, means 25 g of parent isotope is present and 75 g of daughter isotope is present.

This will happen after two half lives i.e 96.2 billion years and after second half life, out of 50 g , 25 g will decay and 25 g will remain.

Thus total 75 g is decayed as daughter isotope and 25 g remains as parent isotope.

1. (1.2kw)x(15/60hours) = .3kwh --> a

2. (5kw)x(90/60hours)x(8cents/kwh) = $0.60 --> d

3. microwave --> 1200 watts = (1.2kw)x(6/60hours) = .12kwh

coffee-maker --> 900 watts = (.9kw)x(10/60hours) = .15kwh

therefore, it requires more energy for the coffee-maker to do the same amount of work.

so the answer is a.

bc blah

explanation:

bc blah