Question

The estimated population of the world was 1.6 billion in 190 and 4.0 billion in 1975. What was the percent increase?

Answer 1

In 1900, there were 1.6bn people,
That means that in 1900 1.6bn was 100%
So,
percent increase is,
`16/10 xx (100+x)/100=4`
`(1600+16x)/1000=4`
`1600+16x=4000`
`16x=2400`
`x=2400/16`
`x=150`
There was a 250% increase.
There was a 250% increase because it is `100+x`

Answer 2

`150%`

Explanation:

In `1990` the population was `1.6` billion (16/10) people. In `1975` it was `4` billion. We need to find the percent increased.

Let it be `x`

We need to build an equation. We know that when we add `x` percent of `1.6` to `1.6`, it gives us `4`

So,

`rarr1.6+1.6xxx/100=4`

`rarr16/10+(16/10x)/100=4`

`rarr(160+16/10x)/100=4`

`rarr160+16/10x=4xx100`

`rarr160+16/10x=400`

`rarr16/10x=240`

`rarrx=cancel240^15xx10/cancel16^1`

`color(green)(rArrx=150%`

Hope this helps!!! ☺•☻