Question

the sum of the ages of two brothers is 21. one is 20 year older than. the other how old are the brothers​

Answer 1

Answer:

Let x be age of older brother now, and y be age of younger brother now

So, equation 1

x + y = 20

Equation 2

x-y = 6

This gives us simultaneous equation. So solve these equations using any of the 3 methods.

The substitution method

The graph method

The subtraction method

I will use the substitution method

From equation 1, we get that X+y=20 therefore making x the subject of the formula x =20-y.

Now since we know that from equation 1 that x = 20-y. we can now run to equation 2 and substitute the new value of x into the equation

So on equation two, x-y=6

So (20-y)-y=6

Hence 20-2y=6, 20-6=2y, 14=2y, so y=7

Now back to equation one

X+y =20, so x+(7)=20,so x=13

Therefore the ages are

Old brother 13 years old

Young brother 7 years old

So the older brother 5 years ago was (13-5) 8 years old