the answer depends on the model that is chosen; could be a linear model or could be an exponential model but the problem statement is missing that information

we can normalize the years by using '1970' as the reference:

1970-1970 = 0

2010-1970=40

we will assume a linear model and solve (entry based on "line equation - two points") the following:

y-0=((40-0)/(1124-742))(x-742)

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click here to solve for the linear equation

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y=(20/191)x - (14840/191)

Now solve for the population in 1990 (normalized to 1990-1970=20:

20=(20/191)x - (14840/191)

click here to solve for the population in 1990

x=933

So based on a linear model the population in 1990 would have been 933.