Question

How can we write an algebraic expression to describe a two digit number whose unit's digit is 5

ess than the ten's digit?
Let's x be ten's digit

Answer 1

required expression = 11x-5

Explanation:

We have information about the following things :

1. Its a two digit number
2. Units digit is 5 less than the tens digit
3. tens digit is x

Since units digit is 5 less than the tens digit, then the unit digit will become

x-5

Now we have these two things:

1. Tens digit is x
2. Units digit is x-5

Now let us look at some two digit numbers like 29 , 43 and 78

in 29, tens digit is 2 and units digit is 9

29 is formed by multiplying the tens digit by 10 and multiplying the units digit by 1 like this : 29 = (2×10) + (9×1)

Similarly;

43 = (4×10) + (3×1)

78 = (7×10)+(8×1)

Now to get out two digit number from the question, we similarly need to multiply the tens digit with 10 and units digit with 1 and add them like this:

tens digit : x

Units digit : x-5

Hence the number is (x × 10) + [(x-5)×1] = 10x + x-5 = 11x-5

hence the required algebraic expression is 11x-5