Question

The doctor prescribes Sally a 210 ml bottle of medicine with the instructions to take 5ml twice a day. How long does the medicine last?
A.one week
B.four weeks
C.Three weeks
D.3 days

Answer 1

Hint: From the given conditions, we will first calculate the amount of medicine to be taken in a day and then we will count the number of days it will last.

Complete step-by-step answer:
We are given that Sally needs to take the prescribed medicine twice a day. The amount which Sally needs to consume of that medicine is 5ml every time.
This implies that Sally needs to take a total of 10ml medicine in a day. ($\because 5ml \times 2 = 10ml$)
So, if we need to calculate the number of days till when the medicine will last, we will divide the total amount of medicine with the amount consumed in a day by Sally.
$ \Rightarrow $The number of days medicine will last= total amount of the medicine prescribed by the doctor the amount of medicine consumed by Sally in a day
$ \Rightarrow $the number of days medicine will last = $\dfrac{{210ml}}{{10ml}}$
$ \Rightarrow $the number of days medicine will last= $21$
So, we can say that medicine will last a total of 21 days.
We can see here that there is no option given as 21 days so we will need to convert the days into weeks.
Now, converting the days into weeks, total weeks = total number of days in a week
$ \Rightarrow $total weeks till the medicine last = $\dfrac{{21}}{7} = 3weeks$
Therefore, option© is correct i.e., the medicine will last 3 weeks.

Note: While solving such sort of questions, you may get confused in the conversion of days to weeks or vice-versa. You need to proceed step by step carefully keeping in mind what we need to solve.