Andy, Peter and Mark took part in a race. The race started at 7.10pm.
Andy took thrice as long as Peter to finish the race and
Mark ws 42min faster than Andy.
If the total time taken by Mark and Andy was 2h30min, what time did Peter
reach the finishing line?


**usually for problem sum, I will minus the more than/heavier than and do this:
150min - 42min = 108min
6unit-108min
1unit-108min/6
=18min

BUT the answer is:-
150min+42min=192min
6unit-192min
1unit-192/6
=32min

Why???

i thot that u should add 42 instead of 48 so the solution would be:
150-42=108
6units=108
1unit would be 108/6=18
Peter would reach the finishing line at 7.28 pm

The answer is 7.42pm as Mark was faster than Andy by 42min. Faster than 42min means less time not more time. Thus Mark's bar should be shorter than Andy. See the solution below.

Thanks for your help. But the answer is 7.42am.
The solution from the assessment book is : 6 units - 2h30min + 42min
= 3h12min
= 192min
1 unit = 192min/6
= 32min (Peter)
Peter reached the finishing line- 7.10am+32min
=7.42am


My answer is also 7.28am......is it printing error???

Sorry, misread the question and included Peter's unit in the total whereas the total given is just Andy and Mark. I have updated the model above.

Yes very clear, thanks very much:)

Btw, when problems sums question ask: eg Melanie is 10kg lighter than Jane. Ruizhen is 8kg heavier than Jane.........

To make the model drawing understand, can i draw
Jane is 10kg heavier than Melanie(as Melanie is 10kg lighter than Jane) and
Ruzhen is 8 kg heavier than Jane.
So that it is easier to solve. Not lighter than n heavier than.
Did my explanation correct???

Yes I understand your explanation. You can change the wording around as long as you keep the same relationship between the two parties the same.

However, do note that this may not always make it easier as the objective of model drawing is to make comparisons in units. So as long as you can establish a certain number of units equates to a particular value then you should be fine. For example, in this question is doesn't mater if we say Mark is faster or Andy is slower. What is important is that to compare Mark to Andy to Peter, we must add the 42 so that we can establish the number of units Mark "has".

Thanks for your explanation.