Question

suppose that the height (in centimeters) of a candle is a linear funtion of the amount of time (in hours) it was been burning. after 15 hours of burning, candle has a height of 24 centimeters. After 28 hours of burning, its height is 18.8 centimeters. what is the height of the candle after 21 hours?

Answer 1

Lets, use an equation

h= kt +b

when t=15, h=24, 24 = 15k +b----i

when t=28, h=18.8, 18.8=28k +b-----ii

24 = 15k +b----i

18.8=28k +b-----ii

lets subtract equation i from ii

(18.8 - 24) = (28k - 15k) + (b - b)

-5.2 = 13k,

k = -0.4

put k= -0.4, into equation i

24=15(-0.4) +b = -6 +b, b= 30

so, h = -0.4t +30

after 21 hours,

h= -0.4(21) +30 = 21.6 centimeters