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A savings pot follows the rule S = 620 - 40w, where S is the amount left in pounds after w weeks. To find the week when the pot runs out, what should be done?
AAdd 620 and 40 and then halve the result
BSet S to zero and solve the rule for w
CSet w to zero and read off the amount left
DDivide 40 by 620 to get the week number
Answer & Solution
Correct answer: B. Set S to zero and solve the rule for w
1. The pot runs out at the moment when the amount left is nothing at all.
2. That is the same as putting the output S equal to zero.
3. Solving 0 = 620 - 40w for w then gives the week number.
4. Option C does the opposite: putting w to zero gives the starting amount of £620, not the finishing week.
5. So set S to zero and solve for w, option B.
_Source: OpenStax College Algebra (CC BY 4.0), Ch 4 "Linear Functions", section 4.1 Linear Functions_
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