70%
For this type of problem we can use a ratio. Using a ratio allows us to to find how much needs to be multiplied by 50 to get 35 (or our percentage needed).
To write the ratio we can say “for every 50 shirts there are 35 once multiplied by a certain percentage”. The ratio would be written out as 35:50. We need to find a way to get 50 to 35 by multiplying (by the percentage). To find the percentage we need to divide 35 by 50. 35/50=0.7.
When working with percentages, decimals will be multiplied by 100 and transferred to a percentage (0.7*100=70 which is then 70%. Multiplying 50 by 0.7 (or 70%) will then give you 35.