Question

At 9:00 a.m. Monday morning, Thomas fills a beaker with water and places it in the corner of the classroom. At 1:00 p.m. on Tuesday, Thomas examines the beaker and notices that the water level is 42 milliliters. At 11:00 a.m. on Wednesday, the water level has dropped to 31 milliliters. If the evaporation of the water follows a linear function, at what time will the beaker be empty?
1:00 a.m. on Thursday
2:30 a.m. on Thursday
1:00 a.m. on Saturday
6:00 a.m. on Saturday

Answer 1

From Tue 1:00 p.m. (42 mL) to Wed 11:00 a.m. (31 mL) is 22 hours and a drop of 11 mL, so the evaporation rate is 11/22 = 0.5 mL/hour.

Go back to Mon 9:00 a.m.: that's 28 hours before Tue 1:00 p.m., so the starting amount was 42 + 28(0.5) = 56 mL.

At 0.5 mL/hour, 56 mL takes 56/0.5 = 112 hours to evaporate. 112 hours after Mon 9:00 a.m. is Sat 1:00 a.m.

Answer: 1:00 a.m. on Saturday.