Question

the mean of three is 10. the mean of other four numbers is 12. Find the mean of all numbers.

Answer 1

As the mean of 3 numbers is 10, the sum of those 3 numbers would have to be 30. This goes the same for the mean of 4 numbers being 12, the sum of those numbers must be 48.

This means that the sum of the two are 30 and 48.

The sum of these is 78, which we can divide by it by the total (which is 7) to get the mean.

so $\frac{78}{7} = 11.14285714$ or $\frac{78}{7}$ if you need the exact value