Question

Change the subject of the formula S = P (1 + rt) to t.

Answer 1

if we're changing the subject to t, we want to get t on it's own.

S = P(1 + rt)

Since we can't do anything with the parenthesis, we have to start with the division/multiplication. Divide both sides by P:

S = 1 + rt
P

Next we want to get rid of the 1, so subtract 1 from both sides:

S - 1 = rt
P

finally, divide both sides by r

(S/P) - 1 = t
r

so:

t = (S/P) - 1
r