Ninety-one 80354

Ninety-one books are arranged on seven shelves so that there are 4 more books on each subsequent shelf than on the previous one. How many books are on the 7th shelf?

Correct answer:

a7 =  25

Step-by-step explanation:

s7=91 d=4  s7 = 2a1+a7 7 s7 = 2a76d+a7 7 s7/7 = a73d  a7=s7/7+3 d=91/7+3 4=25   Verifying Solution:  a1=a76 d=256 4=1 a2=a1+d=1+4=5 a3=a2+d=5+4=9 a4=a3+d=9+4=13 a5=a4+d=13+4=17 a6=a5+d=17+4=21  S=a1+a2+a3+a4+a5+a6+a7=1+5+9+13+17+21+25=91



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