Please help me with the following questions: 1) 25% of 90 is what number? 2) 7% of 80 is what number? 3) What percent 38 is 3.8? 4) 70.6 is what...

Follow these simple steps for each question.

Q1. 25% of 90 is what number?

i) Express 25% as: % (25/100); fraction (¼, when simplified by dividing through with 25); or decimal (0.25, when you divide 25 by 100 or get the inverse of ¼)

ii) Now, you can multiply 90 by any three expressions - 25/100, ¼, 0.25 - to calculate your answer. They should give the same result. Let's check!

25/100 x 90 = 25/100 x 90/1

                    = (25 x 90)/(100 x 1)

                    = 2250/100

                    = 22.5

¼ x 90 = (1 x 90)/(4 x 1)

            = 90/4

            = 22.5

or,

0.4 x 90 = 22.5

Q2. 7% of 80 is what number?

Follow the same steps above and you get: 7/100 or 0.07. Now use (multiply) either 7/100 x 80, or 0.07 x 80 to calculate your answer. Let's calculate then,

7/100 x 80 = 7/100 x 80/1

                  = (7 x 80)/(100 x 1)

                  = 560/100

                  = 5.6

or,

0.07 x 80 = 5.6

Q3. What percent of 3.8 is 38?

i) Define your unknown (%), say x, as an equation.

So your equation becomes: 3.8x = 38.

ii) Now solve for x

3.8x = 38

Isolate x, so

(3.8/3.8)x = 38/3.8

              x = 10

Answer: 10%

iii) Check answer: Substitute x = 10 into the equation: 3.8x = 38, so

3.8x = 38, where x = 10

3.8(10) = 38

       38 = 38

    LHS = RHS so answer is correct!

Q4. 70.6 of what % of 635.4?

i) Apply the same rules as in Q3, so your equation becomes: 70.6x = 635.4

ii) Now solve for x

70.6x = 635.4

Isolate x, so

(70.6/70.6)x = 635.4/70.6

              x = 9

Answer: 9%

iii) Check answer: Substitute x = 9 into the equation: 635.4x = 70.6, so

635.4x = 70.6, where x = 9

70.6(9) = 635.4

   635.4 = 635.4

    LHS = RHS so answer is correct!