Dspace Bhutan by Kinley Penjor

Dspace Bhutan

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Empowering Bhutanese youth with digital education, tech skills, and inspiration in both Dzongkha and English. Join Kinley Penjor's vision for a digitally connected Bhutan.

Thursday, 19 June 2025

Mixed Post

Q. Choden’s Train Trouble

A train 150m long crosses a bridge in 30 seconds at 36 km/h. Find the length of the bridge.

Solution:
Speed = 36 km/h = 10 m/s
Distance = Speed × Time = 10 × 30 = 300 m
Bridge length = 300 − 150 = 150 m

Answer: 150 meters


Q.Sangay’s Geometry Problem

The perimeter of a rectangle is 48 cm, and its length is 4 cm more than its width. Find dimensions.

Solution:
2(l + w) = 48 → l + w = 24
l = w + 4 → w + 4 + w = 24 → 2w = 20 → w = 10 → l = 14

Length: 14 cm, Width: 10 cm


Q.Dema’s Age Puzzle

Dema is twice as old as her sister now. 6 years ago, she was 3 times older. What are their ages?

Solution:
Let sister = x, Dema = 2x
6 years ago: 2x − 6 = 3(x − 6)
2x − 6 = 3x − 18 → x = 12 → Dema = 24

Dema: 24 years, Sister: 12 years


Q.Pema’s Investment (Simple Interest)

Pema invested Nu. 8,000 at 5% per annum for 3 years. What is the total interest?

Solution:
SI = (8000 × 5 × 3)/100 = Nu. 1,200

Answer: Nu. 1,200


Q.Karma's Cylinder Volume

Find the volume of a cylinder with radius 7 cm and height 10 cm. (Ï€ = 22/7)

Solution:
V = Ï€r²h = 22/7 × 7 × 7 × 10 = 1540 cm³

Answer: 1540 cm³


Q.Phub’s Voting Math

In a village, 60% of 1,200 people voted. 70% of those voted for Kinley. How many votes did Kinley get?

Solution:
Votes cast = 60% of 1200 = 720
Kinley's = 70% of 720 = 504 votes

Answer: 504 votes


Q.Choki’s Percent Confusion

A number is increased by 20% and then decreased by 25%. What is the net % change?

Solution:
Let number = 100
Increase → 120
Decrease → 120 − 30 = 90
Change = 90 − 100 = −10%

Answer: 10% decrease


Q.Ugyen's Compound Interest

Ugyen deposited Nu. 10,000 at 10% compound interest for 2 years. Find the final amount.

Solution:
A = P(1 + r/100)^n = 10000(1.1)^2 = 10000 × 1.21 = Nu. 12,100

Answer: Nu. 12,100


Q.Lhamo’s Speed Puzzle

Lhamo drove from Mongar to Bumthang at 60 km/h and returned at 40 km/h. What was her average speed?

Solution:
Average speed = 2ab/(a + b) = 2×60×40 / (60+40) = 4800/100 = 48 km/h

Answer: 48 km/h


Q.Wangchuk’s Profit Ratio

Wangchuk sold a bicycle for Nu. 3,000, making 25% profit. What was the cost price?

Solution:
CP = SP / (1 + profit%) = 3000 / 1.25 = Nu. 2,400

Answer: Nu. 2,400


Q.Sangay’s Equation Mystery

Solve:
(2x3)/5=(x+1)/3(2x - 3)/5 = (x + 1)/3

Solution:
Cross-multiply: 3(2x − 3) = 5(x + 1)
6x − 9 = 5x + 5 → x = 14

Answer: x = 14


Q.Kezang's Remainder Question

What is the remainder when 7⁴ is divided by 5?

Solution:
7⁴ = 2401
2401 ÷ 5 = 480 remainder 1

Answer: 1


Q.Namgay’s Area Puzzle (Trapezium)

A trapezium has bases 8 cm and 12 cm, and height 6 cm. Find its area.

Solution:
Area = ½ × (sum of bases) × height = ½ × (8+12) × 6 = ½ × 20 × 6 = 60 cm²

Answer: 60 cm²


Q.Tshering’s Ratio Challenge

Tshering and Dema share Nu. 800 in the ratio 3:5. How much does each get?

Solution:
Total parts = 3 + 5 = 8
Tshering = (3/8) × 800 = 300
Dema = (5/8) × 800 = 500

Answer: Tshering = Nu. 300, Dema = Nu. 500


Q.Pempa’s Clock Problem

At what time between 3 and 4 o’clock will the hands of the clock be at right angles?

Solution:
Angle = 90°
Formula: θ = |(30H − 11/2)M|
At 3:00 → Hour angle = 90°
Use: 90 = |90 − 11/2 M| → Solve
90 = 90 − 11/2 M → M = 0
or 90 = 11/2 M → M = 16.36

Answer: At 3:16 and 3:49 approx.

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