A contractor estimated that one of his two bricklayers would take 9 hours to build a certain wall and the other 10 hours. However, he knew from experience that when they worked together, 10 fewer bricks got laid per hour. Since he was in a hurry, he put both men on the job and found it took exactly 5 hours to build the wall. How many bricks did it contain?

Therefore the wall contained 900 bricks.

Step-by-step explanation:

Given that there are two bricklayers.

In 9 hours, the first bricklayers built a certain wall and other bricklayer takes 10 hours to build the wall.

Let b = the number of bricks of the wall.

The number brick laid in 9 hour by first bricklayer is b

Then the number brick laid in 1 hour by first bricklayer is .

The number brick laid in 5 hour by first bricklayer is .

The number brick laid in 10 hour by second bricklayer is b

Then the number brick laid in 1 hour by second bricklayer is

Then the number brick laid in 5 hour by second bricklayer is

Again given that, if they worked together 10 fewer bricks got laid per hour.

If they worked together for 5 hours,then (5×10)=50 less bricks were laid by them.

The number of brick were laid by them is .

But the wall made by b number of bricks.

According to the problem,

    [ The L.C.M of 9 and 10 is =10]

Therefore the wall contained 900 bricks.

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step-by-step explanation:

step-by-step explanation:

the original amount doesn't ''re just looking for the time it takes for 1/2 of the substance to we have

(1/2) =)     take the ln   of both sides

ln (1/2)   = )   and we can write

ln(1/2) = ) lne     and lne   = 1     so we have

ln(1/2) = -.1092t     divide both sides by -.1092

t = ln(1/2)/-.1092 = about 6.347 days = about 6.3 days (rounded)