A piece of rope is cut into two smaller pieces, with one piece 90 cm longer than the other . The shorter piece is cut into strips of 20 cm each. The are 20 more strips of 15 cm than20 cm altogether. What is the length of the original piece of rope ?
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Answer
alfretztay
length of shorter pieces : 1u
number of shorter pieces : 1p
total length of longer pieces : (1u + 90)
number of longer pieces : (1p + 20)
1u ——-> 1p x 20 = 20p
(1u + 90) ——-> (1p + 20) x 15 = 15p + 300
20p + 90 = 15p + 300
1p = (300 – 90)/(20 – 15) = 42
42 x 20 + (42 + 20) x 15 = 1770
Ans : 1770 cm.

Something missing in the question.
Maybe the 90 cm longer piece, is cut into strips of 15 cm each?

This is a Quantity Each Product question.
Quantity | Each | Product | |
Short | 1u | 20 | 20u |
Long | 1u + 20 | 15 | 15u + 300 |
30u + 300 |
15u + 300 = 20u + 90
300 – 90 = 20u – 15u
5u = 210
1u = 210 ÷ 5 = 42
30u = 42 ×30 = 1260
1260 + 300 = 1560 cm

UmaPraha
Each short piece is 15 cm length. We tried your method and got solution