Gl assessment test 6

[maznaq]

Question 20;

Which of these statements is always true?
B; if the sum of all the digits in a number is a multiple of four then the number must be a multiple four

C; if the last two digits in a number are a multiple of four then the number must be a multiple of four

The answer is c; why can it not also be b. please help
Many thanks

[Okanagan]

You can disprove B very quickly by considering that you can make a multiple of 4 by adding 1 and 3 or 1 and 7. As 13, 31, 17 and 71 are all odd numbers they clearly aren't a multiple of 4.

[maznaq]

Oh! That makes sense! We kept adding digits of multiple of 4.

I also need help with question 18;
It take 324 kilogram of coal to run a 100 watt lightbulb 24 hrs a day for a year. That equals weight of 3 baby elephant

How many 100 watt light bulbs could run for 12 hrs a day with 11 baby elephant weight of a coal.

[First-timer]

For how long? Seems to be info missing.

[Okanagan]

Assuming this is
"How many 100 watt light bulbs could run for 12 hrs a day (for a year) with 11 baby elephant weight of a coal"

Substitue baby elephants for kilograms and you get
3 baby elephant's weight of coal could run a 100 watt lightbulb 24 hrs a day for a year
which is equivalent to
1.5 baby elephant's weight of coal could run a 100 watt lightbulb 12 hrs a day for a year
so
11 baby elephant's weight of coal could run (11/1.5) 100 watt lightbulbs 12 hrs a day for a year

Answer 7 1/3

[sweethome]

I also find it hard to explain it to my daughter. Does anyone know a simple way of explaining this to a 10 year old?

[parent2013]

Your question: It take 324 kilogram of coal to run a 100 watt lightbulb 24 hrs a day for a year. That equals weight of 3 baby elephant. How many 100 watt light bulbs could run for 12 hrs a day with 11 baby elephant weight of a coal?

It is a very good question and much harder to explain to a 10 year old with the given data. Here's my way of explaining. Note that I have used 12 baby elephant weight of coal instead of 11 for ease of calculation.

Modified question. It take 324 kilogram of coal to run a 100 watt lightbulb 24 hrs a day for a year. That equals weight of 3 baby elephant. How many 100 watt light bulbs could run for 12 hrs a day with 12 baby elephant weight of a coal?

Understanding the question:324 kg coal OR 3 baby elephant equivalent used to burn and provide energey to light "one" 100 watt bulb for 24 hours a day. The question is how many (number of) 100 watt bulb can be lit for 12 hours a day using 12 baby elephant equivalent of coal. The 100 watt of bulb is same & provided just to confuse so you can safely ignore it.

3 baby elephant == to light 1 bulb 24 hours a day

Step 1 Now reduce coal to half the quantity. Why?? To make it equivalent to the question i.e. 12 hours a day.
1.5 baby elephant == to light 1 bulb for 12 hours a day

At this step it is the same bulb and same #hours a day in the question asked

Step 2 Now to the previous step,add 1.5 baby elephant == to light 1 bulb for 12 hours a day which makes
3 baby elephant == to light 2 bulbs for 12 hours a day

Step 3 Now to the previous step, add 3 baby elephant == to light 2 bulb for 12 hours a day which makes
6 baby elephant == to light 4 bulbs for 12 hours a day

Step 4 Now to the previous step, add 6 baby elephant == to light 4 bulb for 12 hours a day
which makes 12 baby elephant == to light 8 bulbs for 12 hours a day

With this understanding, let's do the original question:

3 baby elephant == light 1 bulb 24 hours a day
1.5 baby elephant == light 1 bulb 12 hours a day
Therefore 11 baby elephant == "b" bulb 12 hours a day

b = (11 X 1)/1.5
Answer: 22/3 or 7 1/3

sweethome, maznaq - I hope my explanation helps. Here are some variants of similar question that you can try to test the understanding:[/color]

Q2 It take 3 litres to petrol to run a BMW car for 24 hrs a day. How many days can the BMW car run for 12 hrs every day with 6 litres of petrol?

Data given is
3 litres == 24 hours for 1 day
1.5 litres == 12 hours for 1 day
Question is 6 litres == 12 hours for "d" days

d = (6 X 1)/1.5 [Rule of 3]
Answer: 4 days


[Challenge for our DS's]

Q3 It take 4 hours of charging iPhone to play Minecraft for 6 hrs a day. How many days can you play Minecraft for 12 hrs a day by charging iPhone only once for 24 hours ?

Data given is
4 hours charging == 6 hours playtime for 1 day
8 hours charging == 12 hours playtime for 1 day

Question is
24hours charging == 12 hours playtime for "d" days

d = (24 X 1)/8 [Rule of 3]
Answer: 3 days


Any feedback/criticism of the response is really appreciated
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11 Plus is not difficult to crack. It is all about the way you teach.