2/3 of 1000 kg is fuel, 1/5 is systems; find fraction that

[Jack91]

Im just wondering if any of you could assist me in getting my head around this type of arithmetic. I have a mock paper here from last year and one of the questions on it is:

A spacecraft weighs 1000kg. Fuel accounts for 2 thirds of the weight and another 1 fifth is taken up with casing and guidance systems. What fraction of the weight is taken up altogether with fuel casings and guidance systems? The remainder is a payload of scientific instruments. How much do these weigh?

Now i have tried to work this out and also a friend tried to show me but her way of understanding is totally different than mine. With fractions i like to think of things like a pie when it comes to 1 forth for example. If you could help me work this out i would be much appreciated as maths is a gremlin to me. Thank you folks.

Jack

 

[Mrspi]

Re: Fractions to estimate weight

Hi folks,

Im just wondering if any of you could assist me in getting my head around this type of arithmetic. I have a mock paper here from last year and one of the questions on it is:

A spacecraft weighs 1000kg. Fuel accounts for 2 thirds of the weight and another 1 fifth is taken up with casing and guidance systems. What fraction of the weight is taken up altogether with fuel casings and guidance systems? The remainder is a payload of scientific instruments. How much do these weigh?

Now i have tried to work this out and also a friend tried to show me but her way of understanding is totally different than mine. With fractions i like to think of things like a pie when it comes to 1 forth for example. If you could help me work this out i would be much appreciated as maths is a gremlin to me. Thank you folks.

Jack

You're told that 2/3 of the weight is fuel, and 1/5 of the weight is casing and guidance systems. So, the total fraction of the weight for these two things is

(2/3) + (1/5)

Are you saying you haven't learned to add fractions? In order to add two fractions, they must have the same denominators...because you can only add the same kinds of things.

What is the common denominator for thirds and fifths? The least common multiple of 3 and 5 is 15....so you need to rewrite each fraction as an equivalent fraction with 15 as its denominator.....

Now...see what you can do with that. If you're still having trouble, please repost showing us ALL of the work you've done.

 

[Jack91]

Re: Fractions to estimate weight

Thanks for the reply. With the denominator at 15 i did working out on paper, and i got the answer as the remaining weight is 933.4 kg but cant work out the total weight of fuel casings and guidance systems in a fraction.

 

[Denis]

Re: Fractions to estimate weight

WHAT is the problem?

fuel = 2/3 = 10/15
casing,guidance = 1/5 = 3/15
instruments = 1 - 10/15 - 3/15 = 2/15

10/15 + 3/15 + 2/15 = 15/15 = 1

WHY are you complicating that?

 

[Jack91]

Re: Fractions to estimate weight

Im not delibaretly trying to complicate things you know. I got my head round that i think, so if the remainder payload of instruments weighed 933.4kg that means 66.6kg is the amount i need to convert to a fraction is it? Sorry