the first 30 numbers would be 3,7,11,15,19,23,27,31,35,39,43,47,51,55,59,63,67,71,75,79,83,87,91,95,99,103,107,111,115,119 add these all together you get 1830
So basically you want to find the total percentage of cakes that weren't sponge cakes first.
You already have the 50% of party cakes. For the 1/5 percent of fruit cakes, you can multiply it by 20/20, to get 20/100, and then just take the 20 to get 20% that were fruit cakes.
Now you can just add the percentages together.
50% + 20% = 70%
So now you know 70% weren't sponge cakes, out of 100%.
So here you can just subtract 70% from 100% to figure out the remaining part of 100%, which must be sponge cakes.
She knits 18 squares on Monday. Then she knits 7 more squares each day: Tuesday: +7, Wednesday: +7, Thursday: +7 and Friday: +7 18 + 7 * 4 = 18 + 28 = 46 Answer: She has 46 squares on Friday.