7.8 = 0.65x
x = 100/65 * 78/10
x = 10/5 * 6
x = 12
He ate 15 hot dogs in 3 min.
There are 10 people and you want each of them to have 3 cupcakes. So multiply 10x3, which is 30. Then divide 30 by 8. You can't do that without a remainder though. So you round up to the nearest multiple of 8, which is 32. Then divide 32 by 8, which is 4. So tell dad to bake 4 batches, and the rest is for your dessert tomorrow.
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hope it helps
