Explanation

Calculation:

• Current total age = 80 years

• Three years ago, each person was 3 years younger.

• Since there are three people, the total reduction in age is $3\times 3=9$ years.

So, the total of their ages three years ago is:

$$\mathrm{<b><font\; color="\#0000ff">80</font></b>}<b><font\; color="\#0000ff">-</font></b>\mathrm{<b><font\; color="\#0000ff">9</font></b>}<b><font\; color="\#0000ff">=</font></b>\mathrm{<b><font\; color="\#0000ff">71</font></b>}\text{<b><font color="\#0000ff"> years</font></b>}$$

Explanation

1. Pipe A fills the tank in 15 minutes (rate = $\frac{1}{15}$ per minute).

2. Pipe B fills the tank in 20 minutes (rate = $\frac{1}{20}$ per minute).

3. Combined rate: $\frac{1}{15}+\frac{1}{20}=\frac{7}{60}$ per minute.

4. Time taken together: $\frac{1}{\frac{7}{60}}=\frac{60}{7}$ minutes.

Explanation

25*25 = 625

Explanation

To solve this problem, calculate the total hours worked by the men:

12 men × 8 hours/day × 10 days = 960 hours

Now, find the number of men needed to complete the work in 5 days, working 12 hours a day:

Let x be the number of men.

x men × 12 hours/day × 5 days = 960 hours

x × 60 = 960

x = 16

Explanation

1. Your sister was 4 years old when your brother was born.
2. Your father was 28 years old when your sister was born.
3. So, when your brother was born, your father's age was:

28 (father's age at sister's birth) + 4 (sister's age at brother's birth) = 32