Answer:
Point slope intercept form: The equation for line is given by; ......[1] ; where m is the slope and a point
on the line.
Let x represents the number of days and y represents the number of friends.
As per the statement: After day three, he has 25 friends; after day eight, he has 40 friends.
⇒ We have two points i.e,
(3, 25) and (8, 40)
First calculate slope(m);
Substitute the given values we get;
= 3
now, substitute the given values of m=3 and a point (3, 25) in [1] we get;
Using distributive property;
Add 25 on both sides, we get;
Simplify:
y =3x + 16
if x = 18 days, then;
y = 3(18) + 16 = 54+16 = 70
Therefore, he will have on day 18, if he continues to add the same number of friends each day is, 70 friends.