The histogram presents the compressive strengths of a sample of concrete blocks hardened for 28 days.

One rectangle from the histogram is missing.

What is its height?

The question is not complete but I have uploaded the image to complete the question.

The missing rectangle has a relative frequency of 0.15, and this is the same as the height.

Step-by-step explanation:

Let us define what a frequency and relative frequency are

The frequency of a datum is the number of times a given item (datum) appears in the data set.

While the relative frequency is the fraction or proportion of times taken from the whole in which an item/datum occurs.

So, from the image I uploaded, the relative frequency column represents the height of the histogram. Let the height of the missing rectangle be x.

Therefore the heights of the rectangles written from left to right are 0.05, 0.1, 0.15, x, 0.25, 0.2, and 0.1.

From the definition of relative frequency, the total sum of relative frequency is 1, if represented as decimals or fractions it can either be expressed in percentage, or decimal (fractions). In this question, it is represented in decimal, and the sum of all the relative frequency is 1.

0.05 + 0.1 + 0.15 + x + 0.25 + 0.2 + 0.1 = 1 ;

0.85+ x =1

Therefore, x = 1 - 0.85= 0.15

he spend 5.1 minutes chatting with his friends.

step-by-step explanation:

2/5+1/2=9/10

6/1-9/10=5.1