Explanation

Let's break this down step by step:

1. Let Ali's current age be A and Zia's current age be Z.
2. Since Ali is younger than Zia by 10 years, we can write an equation: A = Z - 10
3. We know that 5 years back, their ages were in the ratio 1:2. So, we can set up another equation based on their ages 5 years back: (A-5)/(Z-5) = 1/2
4. Cross-multiply and simplify the equation: 2A - 10 = Z - 5
5. Substitute the expression for A from step 2 into the equation in step 4: 2(Z-10) - 10 = Z - 5
6. Simplify and solve for Z: 2Z - 20 - 10 = Z - 5 --> Z = 25

So, Zia is currently 25 years old.

Explanation

The mean of 5 observations is 10.

This means the sum of the 5 observations is:

$$\text{Sum of 5 observations}=\text{Mean}\times \text{Number of observations}=10\times 5=50$$

Now, a new observation (10) is added. The new sum becomes:

$$\text{New sum}=50+10=60$$

The new mean of the 6 observations is:

New mean=New sum/Number of observations

​=660​

=10