CBSE Class 10 Maths Arithmetic Progression

maths doubt
 The students of a school decided to beautify the school on the Annual Day by fixing colourful flags on the straight passage of the school. They have 27 flags to be fixed at intervals of every 2 m. The flags are stored at the position of the middle most flag. Ruchi was given the responsibility of placing the flags. Ruchi kept her books where the flags were stored. She could carry only one flag at a time. How much distance did she cover in completing this job and returning back to collect her books? What is the maximum distance she travelled carrying a flag
 A group of men decided to do a job in 8 days. But since 10 men dropped out after 1^{st} day, 2 more men dropped out after 2^{nd} day, 2 more men dropped out after 3^{rd} day and so on, the job got completed at the end of 12^{th} day. How many men were there at the beginning? 55 56 57 58
 Show that (ab)², (a²+b²), (a+b)² are in arithmetic progression.
 Q The angles of a triangle are in AP . the greatest angle is twice the least . Find all angles of a triangle.
 Find three consecutive terms in A.P whose sum is 9 and the product of their cubes is 3375
 Divide 56 into 4 parts which are in AP such that the ratio of product of extreme to the product of the means 5 : 6
 The angles of a quad in ap. With d=10°. Can I not take a3d, ad, a+d, a+3d as the angles. I am getting the angles as 60,80,100,120!!! Value of a=90° after adding the 4 angles.
 The angles of a quand are in A.P with d=10°. Find the angles! (Solution is attached)
 The angles of a quadrilateral are in A.P, and the common difference is 10°. Find the angles. PLEASE TELL ME WHY MY ANSWER IS NOT CORRECT!!!