40 of what number is 20

2 Answers

John P

Nov 10, 2016

200

Explanation:

#40/x = 20/100#
#40/x*100 =20/100*100#

#4000/x = 20#

#4000*x/x =20*x#

#4000 = 20x#

#4000/20 = (20*x)/20#

#200 = x#

Answer link

Suren Abreu

Nov 10, 2016

#200#.

Explanation:

The equation can be expressed as:

#x xx20/100=40#

Multiply both sides by #100/20#.

#x=40xx100/20#

#x=4000/20#

#x=200#

Answer link

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• p% of A = ?
• p% of ? = A
• ?% of A = B
• fractions a/b = ?%
• relative change
• p% = ? number
• (1 + p%) × n
• (1 - p%) × n

40% of what missing number = 20?

Detailed calculations and the verification of the result

A brief introduction. Percent, p%

'Percent (%)' means 'out of one hundred':

40% = 40 'out of one hundred',

p% is read p 'percent',

p% = p/100 = p ÷ 100

40% = 40/100 = 40 ÷ 100 = 0.4

100% = 100/100 = 100 ÷ 100 = 1

What does it mean: Percentage of 40% of which number is equal to 20?

40% of what number = 20

... is equivalent to multiplying them:

40% × number = 20

Number calculation, finding the missing unknown number

Percentage of 40% of what number = 20?

Let y be the number that we have to calculate.

40% × y = 20 =>

y =

20 ÷ 40% =

20 ÷ (40 ÷ 100) =

(100 × 20) ÷ 40 =

2,000 ÷ 40 =

50

40% of 50 = 20

Proof of the calculations

How do we check the result?

We carry out the reverse operation:

If 40% × 50 = 20 =>

Divide 20 by 50...

... And see if we get as a result: 40%

A quick note:

Multiply a number by the fraction 100/100,
... and its value doesn't change.

100/100 = 100 ÷ 100 = 1

n/100 = n%, any number.

Calculate the percentage value: See if we get the percentage of 40%

We will prove below that the calculations are correct.

20 ÷ 50 =

0.4 =

0.4 × 100/100 =

(0.4 × 100)/100 =

40/100 =

40%

The answer:

Percentage of 40% of what number = 20? 40% × ? = 20 40% of 50 = 20

The symbols used: % percent, ÷ division, × multiplication, = the equal sign, / the fraction bar, ≈ approximately the same. Writing numbers: comma ',' - as a thousands separator, point '.' as a decimal mark.

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• p% of what missing number = the given number N?

Three examples of problems that can be solved out using the information in this section:

• Problem 1:

• 25% of the annual profit of a company was invested in buying some new equipment. The total amount invested in buying the new equipment was 100,000 dollars. What was the annual profit of the company?
• Rewrite: 25% of the Profit means 100,000 dollars => 25% × Profit = 100,000 dollars => Profit = 100,000 ÷ 25% dollars = 100,000 ÷ 25/100 dollars = 100,000 × 100/25 dollars = 100,000 × 4 dollars = 400,000 dollars;

• Problem 2:

• 20% of the students in the terminal year have enrolled into the swimming class. In total, 7 students have enrolled. How many students are in the terminal year?
• Rewrite: 20% of the students means 7 students => 20% × Total number of students = 7 => The total number of students = 7 ÷ 20% = 7 ÷ 20/100 = 7 × 100/20 = 7 × 5 = 35;

• Problem 3:

• In the last elections 49% of community memebrs voted for the A Party, 32% for the B Party, and the rest for the C Party. 17,920 people voted for the B Party. How many members are in the community, all in all?
• Rewrite: 32% of the total community members means 17,920 people => 32% × The total number of community members = 17,920 => The total number of community members = 17,920 ÷ 32% people = 17,920 ÷ 32/100 people = 17,920 × 100/32 people = 17,920/32 × 100 = 560 × 100 people = 56,000 people.

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