Math practice for 13 year olds - page 4 of 428
Number of problems found: 8555
- Correcting mean
The average of 10 numbers is calculated as 25. It is later discovered that while calculating the average, the number 36 was wrongly read as 56. Find the correct average. - Two friends 5
Two friends, X and Y: X is 36 years old and Y is 16 years old. In how many years will X be twice as old as Y? - Subtracting 7
Subtracting 50 from 50% of a number gives 50. Find the number. - Rhombus = area, diagonal
The area of a rhombus is 144 cm². One diagonal is twice the length of the other. How long is the shorter diagonal? - Train station
A man walks from his house to the station. If he walks at 5 km/h, he misses a train by 7 minutes. However, if he walks at 6 km/h, he reaches the station 5 minutes before the train departs. Find the distance from his house to the station. - 128 USD
$128 is increased by 20%. Determine the new amount. - Doubling - simple interest A sum of money doubles in 10 years at simple interest. Find the annual interest rate.
- Surface = volume
If the volume and the surface area of a sphere are numerically equal, find its radius. - The radius 4
The radius of a sphere is r = 9 cm. What is the volume of this sphere? Use π ≈ 3.14 and round your answer to the nearest hundredth. - Blue region
Find the area of the blue region shown in the picture. - Collecting money Rs 180 is contained in a box in one-rupee, 50-paise, and 25-paise coins in the ratio 2:3:4. What is the number of 50-paise coins? (One rupee = 100 paise)
- Working group 20 men complete one third of a piece of work in 20 days. How many additional men should be employed to finish the rest of the work in 25 more days?
- 4100 USD $4,100 was distributed among 50 boys and girls. Each boy received $90 and each girl $65. Find the number of boys.
- Somebody Somebody spends 5% of his wages on school fees. That amounts to 800 shillings. How much does he earn?
- By selling 2
By selling 100 pens, a shopkeeper gains the selling price of 20 pens. Find his gain percentage. - 5 yrs 5 years ago, the average age of Rasmi and Suravi was 20 years. Now, the average age of Rasmi, Suravi, and Mita is 30 years. What will be the age of Mita after 15 years?
- Quarter of 60 grams
For a science experiment, students need to find 25% of 60 grams. John says, "I can find this by calculating 1/4 of 60." Andre says, "25% of 60 means 25/100 times 60." Do you agree with either of them? Show your reasoning. - Inverse percentages
If a is 40% of b, what percentage of a is b? - A baseball
A baseball is hit over a fence that is 325 feet away and 110 feet tall. How far did the ball travel in a straight line when it reached the fence? - Fund raising A number of people decided to raise 3 million euros by contributing equal amounts. Had each person contributed 50 euros extra, the total contribution would have been 3.25 million euros. How many people are there?
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