A phone company offers two plans: a prepaid option (6c per second) and a contract option (R25 per month for 200 minutes, then 3c per second). David's call durations today were: 3m 15s, 4m 30s, 45s, 24

First, convert each call duration to seconds:

• $3 \text{ min } 15 \text{ secs} = (3 \times 60) \text{ secs} + 15 \text{ secs} = 180 \text{ secs} + 15 \text{ secs} = 195 \text{ secs}$
• $4 \text{ min } 30 \text{ secs} = (4 \times 60) \text{ secs} + 30 \text{ secs} = 240 \text{ secs} + 30 \text{ secs} = 270 \text{ secs}$
• $0 \text{ min } 45 \text{ secs} = 45 \text{ secs}$
• $0 \text{ min } 24 \text{ secs} = 24 \text{ secs}$
• $12 \text{ min } 10 \text{ secs} = (12 \times 60) \text{ secs} + 10 \text{ secs} = 720 \text{ secs} + 10 \text{ secs} = 730 \text{ secs}$
• $0 \text{ min } 40 \text{ secs} = 40 \text{ secs}$

Now, sum all the durations:

The total time David talked in the day is $\boxed{\text{1304 seconds}}$.

The prepaid option costs 6c per second.
Total seconds from 5.1 = 1304 seconds.
Cost in cents:

Convert cents to Rands (1 Rand = 100 cents):

He would have to pay $\boxed{\text{R}78.24}$.

The Contract option includes 200 minutes.
He gets $\boxed{\text{200 minutes}}$ as part of the Contract option.

For the contract option, calls are billed "per minute or part thereof", meaning each call duration is rounded up to the next whole minute.

• $3 \text{ min } 15 \text{ secs} \rightarrow 4 \text{ minutes}$
• $4 \text{ min } 30 \text{ secs} \rightarrow 5 \text{ minutes}$
• $0 \text{ min } 45 \text{ secs} \rightarrow 1 \text{ minute}$
• $0 \text{ min } 24 \text{ secs} \rightarrow 1 \text{ minute}$
• $12 \text{ min } 10 \text{ secs} \rightarrow 13 \text{ minutes}$
• $0 \text{ min } 40 \text{ secs} \rightarrow 1 \text{ minute}$

Sum the rounded-up minutes:

He would use up $\boxed{\text{25 minutes}}$ on his contract.

a) Why does he say that he only has 22 working days in a month (14 + 8 days = 22 days)?
He states that he uses his free minutes in 8 working days and pays extra for 14 working days. The sum of these two periods ($8 + 14$) represents the total number of working days he considers in a month, which is $\boxed{\text{22 working days}}$.

b) He calculates that he will have to pay for an extra 350 minutes of calls per month. How much extra will he have to pay for calls?
Extra calls are charged at R1.37 per minute.
Extra cost:

He will have to pay an extra $\boxed{\text{R}479.50}$ for calls.

c) Using your answer from question 5.5 b), calculate his total that he would pay per month for the Contract option.
Monthly fee for Contract option = R381.90.
Extra call cost from 5.5 b) = R479.50.
Total monthly cost for Contract option:

He would pay a total of $\boxed{\text{R}861.40}$ per month for the Contract option.

This question asks for the cost of the calls made in 5.1 if the Prepaid option was used. This is the answer from question 5.2.
He would pay $\boxed{\text{R}78.24}$ per month for his calls if he used the Prepaid option.

Compare the total monthly costs:

• Prepaid option (from 5.6): R78.24
• Contract option (from 5.5 c): R861.40

The Prepaid option is significantly cheaper for the calls David made.
I would advise him to choose the $\boxed{\text{Prepaid option}}$.
Reason: The total cost for his calls using the Prepaid option (R78.24) is much lower than the total cost for the Contract option (R861.40), even considering the monthly fee and extra minutes.

Worksheet 6

a) How far does she ride in mm?
Mary-Jane rides 14.84 km.
To convert kilometers to millimeters:
$1 \text{ km} = 1000 \text{ m}$
$1 \text{ m} = 1000 \text{ mm}$
So, $1 \text{ km} = 1000 \times 1000 \text{ mm} = 1,000,000 \text{ mm}$.
Distance in mm:

She rides $\boxed{\text{14,840,000 mm}}$.

b) Which unit (km or mm) do you think is best for measuring this distance?
$\boxed{\text{Kilometers (km)}}$ is the best unit for measuring this distance. Millimeters would result in a very large and impractical number, while kilometers provide a more manageable and understandable value for such a long distance.

a) How many ml of orange juice can it hold?
The vat holds 4600 L of orange juice.
To convert liters to milliliters:
$1 \text{ L} = 1000 \text{ ml}$
Volume in ml:

It can hold $\boxed{\text{4,600,000 ml}}$ of orange juice.