World Population

Question

In 2013 the membership for The Church of Jesus Christ of Latter-day Saints reached 14,780,000 members.

In 1990 the membership for The Church of Jesus Christ of Latter-day Saints was 7,300,000 members.

Letting t = 0 represent the year 2013 and assuming the church membership continues to double about every 23 years, predict church membership in year 2075.

(Round to the nearest whole number and do not use commas.)

Answer 1

Let's use the rule of 70 to estimate this.  The rule of 70 says that the growth rate in % per some amount of time, times the number of periods of that amount of time, equals approximately 70.

For example, if a bank account is giving around 1% annual interest per year, it would take around 70 years for the money in the account to double.

So if the membership is doubling every 23 years, what is the growth rate?  To find it, divide 70 by 23, which is around 3.04% per year.

 

So let's use that growth rate to estimate the membership in 2075.

 

That's 62 years after the starting year of 2013.  The formula for this is A(1+r)ⁿ, where A is the starting number, r is the growth rate, and n is the number of years.  So the membership in 2075 would be 14780000(1+3.04%)⁶² = 14780000(1.0304)⁶².  That's a messy number, but it can be done easily on a calculator, with the result being 94631807.43.  Rounded to the nearest whole number, it is 94631807.