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Mathematics

1 answer:

Valentin [98]3 years ago

7 0

Answer:

Todd: 25
Andrew: 45

Step-by-step explanation:

We can let "a" stand for the number of goldfish Andrew has. Then the number Todd has is (70-a). We are told the difference is ...

a - (70-a) = 20

2a = 90 . . . . . . . .collect terms, add 70

a = 45

70-a = 25

Andrew has 45 goldfish; Todd has 25.

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Comment on the problem

I call this a "sum and difference" problem. You are given the total of two counts, and also their difference. If you were paying attention to the above solution, you see that the larger of the counts is (70+20)/2, half the sum of the given numbers. This is generically true of all sum and difference problems.

Knowing this, you can work most of these problems in your head.

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The box which measures 70cm X 36cm X 12cm is to be covered by a canvas. How many meters of canvas of width 80cm would be require

grigory [225]

Answer:

142.2 meters.

Step-by-step explanation:

We have been given that a box measures 70 cm X 36 cm X 12 cm is to be covered by a canvas.

Let us find total surface area of box using surface area formula of cuboid.

$\text{Total surface area of cuboid}=2(lb+bh+hl)$ , where,

$l$ = Length of cuboid,

$b$ = Breadth of cuboid,

$w$ = Width of cuboid.

$\text{Total surface area of box}=2(70\cdot36+36\cdot 12+12\cdot 70)$

$\text{Total surface area of box}=2(2520+432+840)$

$\text{Total surface area of box}=2(3792)$

$\text{Total surface area of box}=7584$

Therefore, the total surface area of box will be 7584 square cm.

To find the length of canvas that will cover 150 boxes, we will divide total surface area of 150 such boxes by width of canvass as total surface area of canvas will also be the same.

$\text{Width of canvas* Length of canvass}=\text{Total surface area of 150 boxes}$