Question

in the video game gemetric constructors a number of the shapes have to be arranged into a predefined form , in level 1, you are given 3 min 20s to complete the task, at each level afterward, a fixed number of seconds are removed from the time until, at level 20 , 1 min 45s are given, what would be the total amount of time given if you were to complete the first 20 levels

Answer 1

look at it as an arithmetic sequence , where
term(1) = 3 min , 20s or 200 sec
term(20) = 1 min, 45 sec or 105 seconds

a = 200
a + 19d = 105
subtract..
19d = -95
d = -5

so sum(20) = (20/2)[2(200) + 19(-5)] = 3050 seconds
= 50 min, 50 seconds

Answer 2

Thanks:)