Question

In math, how to know when to add an alphabet, Let say assume this value to be x or y. how to understand when to assume???

please help with a detail understanding​

Answer 1

So let's understand with an easy example.

Suppose, a number when added to 7 gives 13.

Now, here, we know that if a number is added to 7, we get 13. But we don't exactly know what the number is. So, we assume the number by any variable. We can assume the number to be x, y, z, a, b, c anything.

Hence, after assuming, we get

x + 7 = 13

→ x = 13 - 7 (when transporting number to other side, their symbol changes. + changes to -. - changes to +. × changes to ÷ and ÷ changes to ×.)

→ x = 6

Hence, the number required is 6.

Another example may clear it more.

Suppose, we are asked to find a number whose twice when added to 6, gives 30.

Now, again, we don't know what number's twice is added to 6 to give 30.

Hence, assume it to be any alphabet. Let it be "a" this time.

Then, 2a + 6 = 30 (since, twice of the number is added to 6 to give 30)

→ 2a = 30 - 6

→ 2a = 24

→ a = 24 ÷ 2

→ a = 12

Answer 2

Answer:

See we add variables only when value is not given ....

Take an example - jungkook bought 2 pens and 4 pencil for rs 10 and suga bought 8 pens and 1 pencil for rs 20. Find the cost of each pen and pencil ....(just an example i don't know if its correct or not ) .

So here we are not given the cost of single pencil or pen we can take

1 pen= x rs

1 pencil = y rs

Here you can form equation as

2x + 4y = 10...............(1)

8x + 1y = 30.............(2)

Hope u got it .....