Problem 1 :
Find 24% of 20.
Problem 2 :
What percent of 80 is 20?
Problem 3 :
88 is what % of 160?
Problem 4 :
30% of what number is 21?
Problem 5 :
50 is 0.4% of what number?
Problem 6 :
The price of a product is increased from $90 to $108. Find the percent increase.
Problem 7 :
In a library there are 1500 books in which 1125 are English books and the rest are Spanish books. Find the percent of Spanish books in the library.
Problem 8 :
A product is sold at 10% discount and there is 5% sales tax on the discounted price. If a customer pays $113.40 for the product, find its original.
Problem 9 :
Jewelers use the karat system to determine the amount of pure gold in jewelry. Pure gold is 24 karat, meaning the item is 100% gold. A 14.4-karat gold ring contains 14.4 parts gold and 9.6 parts other metal. What percent of the ring is gold?
Problem 10 :
A chemist has 20 milliliters of a solution that is 40% acid. She wants to increase the acid content of the solution to make it a 50% acid solution. How many milliliters of pure acid should she add to the solution?
Problem 11 :
In the first 20 days of a month, a sales man has made $2,550 sales which is 85% of his monthly target. Find the monthly target.
Problem 12 :
A student has scored 450 marks which 45 marks more than the pass marks. If each student has to secure 45% of the total marks to pass the exam, find the total marks in the exam.
1. Answer :
24% of 20 :
= (²⁴⁄₁₀₀)(20)
= 0.24(20)
= 4.8
2. Answer :
Let x percent of 80 be 20.
x% of 80 = 20
(ˣ⁄₁₀₀)80 = 20
⁴ˣ⁄₅ = 20
Multiply both sides by 5.
4x = 100
Divide both sides by 4.
x = 25
Therefore, 25 percent of 80 is 20.
3. Answer :
Let 88 be x% of 160.
88 = x% of 160
88 = (ˣ⁄₁₀₀)160
88 = ⁸ˣ⁄₅
Multiply both sides by 5.
440 = 8x
Divide both sides by 8.
x = 55
Therefore, 88 is what 55% of 160.
4. Answer :
Let 30% of x be 21.
30% of x = 21
(³⁰⁄₁₀₀)x = 21
(³⁄₁₀)x = 21
Multiply both sides by 10.
3x = 210
Divide both sides by 3.
x = 70
Therefore, 30% of 70 is 21.
5. Answer :
Let 50 be 0.4% of x.
50 = 0.4% of x
50 = (⁰^{.}⁴⁄₁₀₀)x
Multiply both sides by 100.
5000 = 0.4x
Divide both sides by 0.4.
12,500 = x
Therefore, 50 is 0.4% of 12,500.
6. Answer :
Percent increase :
= 20%
7. Answer :
Total number of books = 1500
Number of English books = 1125
Number of Spanish books :
= 1500 - 1125
= 375
Percent of spanish books in the library :
= 25%
8. Answer :
Let x be the original price of the product.
After 10% discount, the price of the product :
= (100 - 10)% of x
= 90% of x
= 0.9x
After 5% sales tax on the discounted price, the price of the product :
= (100 + 5)% of 0.9x
= 105% of 0.9x
= 1.05(0.9x)
= 0.945x
Given : After 10% discount 5% sales tax on the discounted price, a customer pays $113.40 for the product.
0.945x = 113.40
Divide both sides by 0.945.
x = 120
Therefore, original price of the product is $120.
9. Answer :
Given : A 14.4-karat gold ring contains 14.4 parts gold and 9.6 parts other metal.
Percent of gold in the ring :
= 60%
10. Answer :
Amount of acid in 20 milliliters of a solution that is 40% acid :
= 40% of 20
= 0.4(20)
= 8 milliliters
Let x milliliters of pure acid should be added to 20 milliliters to get a 50% acid solution.
Now, amount of acid in the resulting solution :
= (8 + x) milliliters
Given : Resulting solution is a 50% acid solution.
8 + x = 50% of (20 + x)
8 + x = 0.5(20 + x)
8 + x = 10 + 0.5x
0.5x = 2
x = 4
Therefore, the chemist should add 4 milliliters of pure acid to make it a 50% acid solution.
11. Answer :
Let x be the monthly target.
Given : 85% of the monthly target is $2,550.
85% of x = 2550
0.85x = 2550
x = 3000
Therefore, the monthly target is $3,000.
12. Answer :
Let x be the total marks in the exam.
Given : 450 marks is 45 marks more than the pass marks and a student has to secure 45% of the total marks to pass the exam.
45% of x = 450 - 45
0.45x = 405
x = 900
The total marks in the exam is 900.
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