The variable y is the number of bicycles sold (in millions) and x is the number of years since 1981. We are given an equation which relates these variables.
y=0.3x+15
We want to find in what year 22 million bikes had been sold. First, we will need to find the value of x when y=22. Let's substitute y=22 into the equation.
22=0.3x+15
Let's use a table to estimate the number of years x.
x
22=0.3x+15
Simplify
Close estimate?
1
22? ≈0.3* 1+15
22 ≈ 15.3
No way
10
22? ≈0.3* 10+15
22 ≈ 18
Nope
20
22? ≈0.3* 20+15
22 ≈ 21
Getting closer...
25
22? ≈0.3* 25+15
22≈ 22.5
Oops, went too far
24
22? ≈0.3* 24+15
22≈ 22.2
Still too far!
23
22? ≈0.3* 23+15
22≈ 21.9
Must be this one
24 years after 1981 the bicycle company sold more than 22 million units. 23 years after 1981, the company sold just under 22 million bicycles. We can interpret this information to say that sometime during the 23rd year after 1981, 22 million bicycles had been sold. To find the desired year we need to add 23 to 1981.
1981+23=2004
22 million bicycles were sold in 2004.
