SOLUTION: In a certain spider web, the lengths of the shortest and longest threads are 3.4mm and 50.2mm respectively. The successive equally spaced threads are 1.2mm apart. If the length of

Question 1203960: In a certain spider web, the lengths of the shortest and longest threads are 3.4mm and 50.2mm respectively. The successive equally spaced threads are 1.2mm apart. If the length of the cross threads form an Arithmetic Progression (A.P), find the number of cross threads.
Found 2 solutions by mananth, greenestamps:
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!

In a certain spider web, the lengths of the shortest and longest threads are 3.4mm and 50.2mm respectively. The successive equally spaced threads are 1.2mm apart. If the length of the cross threads form an Arithmetic Progression (A.P), find the number of cross threads.
Length of the shortest thread are 3.4mm
Length of the longest thread are 50.2mm
The successive equally spaced threads are 1.2mm apart
length of the cross threads form an Arithmetic Progression
Here a 3.4 , tn = 50.2 d= 1.2
tn = a+(n-1)*d
50.2= 3.4+ (n-1)* 1.2
50.2 - 3.4 = (n-1)*1.2
46.8= (n-1) *1.2
46.8/1.2= n-1
39 = n-1
n=40
The number of cross threads =40

Answer by greenestamps(13200) (Show Source): You can put this solution on YOUR website!

You should understand the formal algebra that can be used to solve the problem, as shown in the response from the other tutor. But I believe students will understand how to work problems involving arithmetic progressions better if they are able to work the problem informally -- which helps them understand WHY the formal algebra works.

If we subtract the shortest thread length from the longest and divide the result by the difference between the lengths of successive threads, we get the number of threads AFTER THE FIRST ONE.

(50.2-3.4)/1.2 = 46.8/1.2 = 39

So the number of threads is 39+1 = 40.

ANSWER: 40

RELATED QUESTIONS
I AM A GRANDFATHER TRYING TO HELP MY GRANDSON WITH ALGEBRA 1A. I HAVE SEVERAL PROBLEMS I... (answered by MathLover1)
The arc of a spider web is 1/4 of a circle and 20 in. in length. Calculate area of web in (answered by Theo)
In a triangle, the middle length side is 3 more than the shortest side, and the longest... (answered by shree840)
The lengths of the sides of a triangle are 6, 7, and 9. Find the longest side of a... (answered by tommyt3rd)
On a photograph of a triangular piece of land, the lengths of the three sides are... (answered by josmiceli)
The lengths of the sides of a triangle are 12,15,and 20.If the length of the shortest... (answered by edjones)
Two angles in a triangle are 49 and 61. If the longest side of the triangle is 15 cm... (answered by Fombitz)
The lengths of the sides of a triangle are 3, 4, and 6. If the length of the shortest... (answered by TimothyLamb)
A certain triangle has a perimeter of 3082mi. The shortest side measures 79mi less than... (answered by macston)