Explanation

Given:

• Train length = 90 m
• Tunnel length = 231 m
• Time = 11 seconds

Distance covered = 90 + 231 = 321 m

Speed = Distance ÷ Time
= 321 ÷ 11 = 29.18 m/s

Convert to km/h:

29.18 × 18/5 = 105.05 km/h

Explanation

1. Current Ages:

   • Let Zoya’s current age be $x$
   • Then, Zaid’s current age is $6x$ (since he is six times as old as Zoya).

2. The sum of Ages in 7 Years:

   • In 7 years, Zoya's age will be $x + 7$ and Zaid's age will be $6x + 7$.
   • The sum of their ages in 7 years will be $(x+7)+(6x+7)=49$.

Step 1: Formulate the Equation

x+7+6x+7=49
$$7x+14=49$$

Step 2: Solve for $x$

Subtract 14 from both sides:

$$7x=35$$

Now divide by 7:

$$x=5$$

So, Zoya’s current age is $5$ years and Zaid’s current age is:

$$6x=6\times 5=30$$

Step 3: Determine Zaid’s Age When Zoya Was Born

When Zoya was born, Zaid would have been:

$$30-5=25$$

Explanation

Let daughter age = x

Father age = 5 times daughter age = 5x

Sum of ages = 50

x + 5x = 50

6x = 50

x = 50 / 6 = 8.33

So daughter = 8.33 years

Father = 5 x 8.33 = 41.67 years

Last verified on 02-09-2026

Explanation

Use the set formula: 

Students who study CS or Math = CS + Math - Both  

= 55 + 50 - 10  

= 95 students

Students who study neither = Total students - Students who study CS or Math  

= 100 - 95  

= 5 students

Last verified on 02-09-2026

Explanation

Father’s current age = 72 − 6 = 66 years.

Son’s current age = 66 ÷ 6 = 11 years.

Last verified on 02-09-2026

Explanation

Given: Father's age = 5 times daughter's age = 5x years

Sum of ages = 48 years

So, x + 5x = 48

6x = 48

x = 48 / 6

x = 8

Daughter's current age = 8 years

Last verified on 03-08-2026

Explanation

Let the younger brother's present age = x years

Then older brother's present age = x + 9 years

After 5 years:

Younger brother's age = x + 5

Older brother's age = x + 9 + 5 = x + 14

Sum after 5 years = 49

So, (x + 5) + (x + 14) = 49  

2x + 19 = 49  

2x = 49 - 19  

2x = 30  

x = 15

Younger brother = 15 years  

Older brother = x + 9 = 15 + 9 = 24 years

Last verified on 04-09-2026

Explanation

Let the son's age = x years

Mother's age = 5 times son's age = 5x years

Sum of their ages = 60 years

So, x + 5x = 60

6x = 60  

x = 60 / 6  

x = 10

Son's present age = 10 years

Last verified on 04-09-2026

Explanation

Total work = people × days = 500 × 25 = 12500 person-days

Work done in first 12 days by 500 people = 500 × 12 = 6000 person-days

Remaining work = 12500 - 6000 = 6500 person-days

Now 300 people will do the remaining work.  

Days needed = Remaining work / people = 6500 / 300 = 21⅔ days

Last verified on 05-09-2026

Explanation

Let son's age = x. Then mother's age = 3x because it is 3 times the son's age.

Sum of ages = 70, so x + 3x = 70 → 4x = 70.

Solve: x = 70 ÷ 4 = 17.5. So son's present age = 17.5 years

Last verified on 05-09-2026