1. The sum of a two-digits number is 13. The tens digit is 8 less than twice the units digit. What is the number?

The number is 67

Step-by-step explanation:

Equations

Let's consider the number 83. The tens digit is 8 and the unit digit is 3. Note the tens digit's addition to the number is 80, and the unit's addition is 3. This means the tens digit adds 10 times its value, that is, 83 = 8*10 + 3.

Now, let's consider the number ab, where a is the tens digit, and b is the unit digit. It follows that

Number=10*a+b

The question gives us two conditions:

1) The sum of a two-digits number is 13.

2) The tens digit is 8 less than twice the units digit.

The first condition can be expressed as:

a + b = 13                     [1]

And the second condition can be written as:

a = 2b-8                      [2]

Replacing [2] into [1], we have:

2b-8 + b = 13

Operating:

3b = 13 + 8

3b = 21

Solving for b:

b = 21 / 3 = 7

Substituting into [2]:

a = 2*(7) - 8 = 6

Thus, the number is 67

the largest number of the four options is 1.8 x 10-2

you have it in scientific notation.

1.80 x 10-6   = 0.00000180

1.80 x 10-4   = 0.000180 (bigger, or "less small", than the former one)

so

1.8 x 10-2       = 0.0180. as you see. the "less small", or the biggest one of them all.

as you have negative exponent, it means you are dividing 1.8 by 100 (i.e. moving the dot towards left, two times).

if you had positive exponent for the scientific notation, power of tenths, you would be multiplying times 100 (moving the dot towards right) as below:

1.8 x (10)2 = 180

so. if you have negative exponent in scientific notation, move the dot toward left. if it is positive, toward right as many times the exponent tells you.