A video game's battery indicator estimates the remaining charge , in percent, with the model
where is the number of hours the game console has been used since it was fully charged, for . According to the model, what percent of battery charge remains after the console has been used for hours?
A linear model with a starting amount and a change per hour lets you predict an amount at a given time. If the question gives the hours and asks for the remaining percent, the hours are the input. Put that time into the rule and evaluate it in Desmos. Don’t confuse the amount used with the amount left.
Hints
- Hint 1
The input is the value you put into a model. The question gives hours of use, so which letter represents the time? What number should replace that letter?
- Hint 2
The term counts the charge used after hours. The model subtracts it from the starting charge. Which quantity does that leave you with?
Step-by-step
Substitute and evaluate in Desmos
Step 1Put the time into the model
Here is the input, the number of hours used. The question gives 18 hours, so replace with :
Hours go in; remaining battery percent comes out. The part counts charge used, not charge left.
- Step 2
Enter the battery rule
Type in Desmos. Writing makes the given model a function, a rule you can use with a time on the next line. Desmos stores this battery rule.
- Step 3
Read the remaining charge
Type on the next line. Desmos displays . That’s the output, so 28% of the battery charge remains after 18 hours. Choice C.