The mean of a set of 5 numbers is 26. What would the mean be if one of the numbers was increased by 10?

I don't think that that answer is correct, Anonymous....if one number increased by 10, we couldn't have a mean that was less than before...!!

The correct answer is that the mean would increase by 2......(130 + 10) / 5 = 140 / 5   = 28  ....!!!

sum of terms=$${\mathtt{26}}{\mathtt{\,\times\,}}{\mathtt{5}} = {\mathtt{130}}$$

new mean=$${\frac{\left({\mathtt{130}}{\mathtt{\,\small\textbf+\,}}{\mathtt{10}}\right)}{{\mathtt{6}}}} = {\frac{{\mathtt{70}}}{{\mathtt{3}}}} = {\mathtt{23.333\: \!333\: \!333\: \!333\: \!333\: \!3}}$$(as 1 term increased so 5+1 )

easy one!!!!!!!!!!!!!!